Hubbry Logo
Threaded insertThreaded insertMain
Open search
Threaded insert
Community hub
Threaded insert
logo
8 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Threaded insert
Threaded insert
Threaded insert
View on Wikipedia
from Wikipedia
TIME-SERT insert

A threaded insert, also known as a threaded bushing or insert nut, is a fastener element that is inserted into an object to add a threaded hole.[1] They may be used to repair a stripped threaded hole, provide a durable threaded hole in a soft material, place a thread on a material too thin to accept it, mold or cast threads into a work piece thereby eliminating a machining operation, or simplify changeover from unified to metric threads or vice versa.[2]

In woodworking, an insert nut provides a threaded socket for a wooden workpiece, similar to a wall anchor. Insert nuts are inserted into a pre-drilled hole by one of two means: screw in and hammer in. In both cases, the external protrusions bite into the wood, preventing the nut from either turning or pulling out.

Types

[edit]

Thread inserts come in many varieties, depending on the application. Threaded inserts for plastics are used in plastic materials and applied with thermal insertion or ultrasonic welding machines.

Manufacturers of ready-to-assemble furniture often ship the parts with threaded inserts and other kinds of knock-down fasteners pre-installed.

People who use sheet metal or sandwich panel or honeycomb sandwich-structured composite often install threaded inserts to spread shear, tension, and torque loads over a larger area of the material.[3]

Captive nut

[edit]

Captive nuts come in two basic styles. One type, the cage nut or clip-on nut is a conventional nut held captive by a sheet metal carrier that clips onto the part to be connected. These are generally used to attach screws to sheet metal parts too thin to be threaded, and they can generally be attached, removed and reused with simple hand tools.

The second type of captive nut is a threaded insert. These are either pressed into holes in the material to be joined or moulded in. In either case, part of the insert is generally knurled to get a good grip on the material supporting the insert. One variant, the swage nut, has a knurled portion that swages the sides of a soft metal hole to more tightly grip the nut. Press fit and swaged captive nuts are used in panels that are too thin to be threaded or in soft materials that are too weak to be threaded. They are installed by pressing them in with an arbor press.[4]

Threaded inserts are commonly used in plastic casings, housing, and parts to create a metal thread (typically: brass or stainless steel) to allow for screws to be used in the assembly of many consumer electronics and consumer products. These may be cast in place in injection molded parts or they may be added by thermal insertion. In the latter, the insert is heated and then pressed into a hollow in the plastic part. The heat causes local melting in the plastic.[5] Ultrasonic Insertion is the process used to apply vibration and pressure to install the threaded insert into a molded hollow boss (hole) of a plastic part. The ultrasonic vibrations melt the thermoplastic material where the metal insert is in contact, and pressure is applied to press it into position. The material typically reforms around the knurled body of the threaded insert to ensure a good retention.

Externally-threaded inserts

[edit]
A self-tapping insert

An externally threaded insert has threads on the outside and inside. The insert can be threaded into a pre-tapped hole, or a self-tapping insert creates its own threads in a drilled or molded hole. It is then anchored by various means, such as a nylon locking element. Inserts that are anchored via Loctite are more commonly known by the trademarked name E-Z Lok.[6] A thin-walled solid-bushing insert by the trademarked name TIME-SERT is locked in by rolling the bottom few internal thread into the base material with a special install driver which will permanently lock the insert in place.[citation needed] Key-locking inserts, more commonly known by the trademarked name Keenserts, use keys that are hammered into grooves through the threads, permanently locking the insert.[7][8][9] Inserts that are self-tapping and lock via friction are more commonly known by the trademarked names Tap-lok or Speedserts.

Helical insert

[edit]
A helical insert. The straight radial piece is the driver tang which is used to grip the coil while driving it into place. It is broken off and is discarded after installation.

A helical insert (also called a screw thread insert (STI), although most users call them all by one of the prominent brand names: KATO®, Heli-Coil® or Recoil®) is an insert made of stainless steel or phosphor bronze wire, with a diamond cross section, coiled to form inner and outer threads. The coil of wire screws into a threaded hole, where it forms a smaller-diameter internal thread for a screw or stud.[10] These inserts provide a convenient means of repairing stripped internal threads. These inserts are commonly sold in kits with matched taps and insert tools.

In soft materials, they are used to provide stronger threads than can be obtained by direct tapping of the base materials, e.g. aluminium, zinc die castings, wood, magnesium, plastic.

An example application is engine repair after unintentionally destroying the threads in a socket for a spark plug by over-torquing or cross-threading.

Mold-in inserts

[edit]

A mold-in insert has a specially shaped outer surface to anchor the insert in plastic. For injection-molded plastic, the insert is placed in a mold before it is filled with plastic, making an integral part. An insert can also be heated and pressed into pre-made thermoplastic material.[11]

For softer, more pliable plastics, hexagonal or square inserts with deep and wide grooves allow the softer plastics to hold the inserts sufficiently. The process allows large product manufacture i.e. fuel tanks, boats etc., so the torque inserts may be of large thread sizes.

Press-fit inserts

[edit]

A press-fit insert is internally threaded and has a knurled outer surface. It is pressed into a plain hole with an arbor press.[11]

Potted inserts

[edit]

A potted insert is set in epoxy to fix it, such as in a honeycomb sandwich panel, often used in commercial aircraft, and is said to be potted in.

Rivet nut

[edit]
Main article: Rivet nut

A rivet nut, also known as a blind rivet nut, or rivnut, is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side.

Strength factors of threaded inserts

[edit]

Pull-out resistance & torque-out resistance are the two main strength factors of threaded inserts.

  • Pull-out resistance: the force required to begin to pull the insert out of the parent material
  • Torque-out: the amount of torque required to begin to turn the fastener

Installation methods

[edit]
Rampa- or screw-in nut

For industrial purposes, the following installation methods are the standards:

  • Thermal insertion
  • Injection molding
  • Manual pressing

For craft purposes, they might be:

  • Screw-in type: Screw-in insert nuts have an external thread and hex head and are screwed in with a Flat Blade Screwdriver or an Allen wrench. The screw-in insert nuts come in various sizes and take different screw sizes. For example, an M6 insert nut will take an M6 bolt, a "1/4-20" insert nut will take a 1/4-20 inch bolt., etc The pre-drilled hole must be as deep as the length of the insert nut plus any portion of the bolt that may be screwed past the end of the nut in the work piece.
  • Hammer-in type: Hammer-in insert nuts, also known as knock-in nuts,[citation needed] are lined with barbs and are hammered in. They are often made of steel, brass or nylon. They are designed to work in wood and particle board.[12]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Threaded insert

View on Grokipedia
from Grokipedia
A threaded insert is a cylindrical metal component that is inserted into a in a base material—such as , , or soft metals—to provide a durable, reusable internal thread for securing screws or bolts, thereby preventing thread stripping in materials that cannot reliably hold direct threading. These inserts are engineered to distribute fastening loads over a larger area, enhancing the strength and longevity of assemblies in challenging substrates. Common types include press-fit inserts, which rely on friction and knurls for retention; heat-set inserts, installed via ultrasonic or thermal methods for thermoplastics; helical inserts like Heli-Coil, which coil into place to repair or reinforce threads; mold-in inserts, embedded during the molding process; and externally threaded inserts, which screw into the host material. Each type is selected based on factors such as material compatibility, installation environment, and load requirements. Threaded inserts were developed in the 1930s for the and sectors to provide durable threads in lighter and softer materials used in , where resistance and reliability are critical. Today, they are essential across diverse industries, including automotive for and assemblies, for circuit board mounting, furniture for reinforcement, and general for repairing stripped holes or enabling disassembly. Their key advantages include superior pull-out and resistance compared to direct threading in soft materials, facilitation of multiple assembly cycles without degradation, and compatibility with automated installation processes.

Fundamentals

Definition and Purpose

A threaded insert is a cylindrical or similarly shaped component featuring internal threads designed to be embedded into a base material, thereby creating a durable, reusable threaded hole for securing screws, bolts, or other male-threaded fasteners. These inserts serve as specialized bushings that integrate seamlessly with the host material, offering a reliable connection point without requiring the base to support threads directly. The primary purpose of threaded inserts is to overcome the challenges associated with threads directly into softer, more brittle, or composite s, where standard threading often leads to stripping, cracking, or insufficient load distribution. By encapsulating and reinforcing the threaded interface, inserts enhance overall integrity, allow for repeated assembly and disassembly, and mitigate risks of under or . This makes them essential in applications demanding high-strength fastening in materials ill-suited for conventional threads, such as plastics, wood, or lightweight alloys. In terms of basic anatomy, threaded inserts typically include external retention features like knurls for mechanical grip or flanges for axial positioning and load distribution, paired with precisely machined internal threads that conform to standardized specifications, including Unified National Coarse (UNC), Unified National Fine (UNF), or metric sizes. These design elements ensure secure embedding and compatibility with common fasteners, facilitating efficient installation and performance. Threaded inserts evolved in response to early 20th-century demands in and machinery, where reliable fastening in non-metallic or low-strength components became critical for safety and efficiency. Pioneered in the 1930s to address stress concentrations in threads, they provided a solution for embedding strong, wear-resistant connections in challenging materials. Forms such as helical coils or solid bodies emerged to fulfill this role across diverse engineering needs.

Historical Development

A significant advancement occurred in the 1930s within the sector, where the need for stronger threads in high-stress environments drove innovation. In 1939, engineer Harold Caminez developed the helical wire thread insert, initially known as the Aero-Thread Screw Thread System, to mitigate notch effects and stress concentrations in threads, such as those in Allison engines. This design was first commercially applied in engines by late 1939 and soon adopted by other manufacturers including Lycoming and . By 1942, the insert was renamed Heli-Coil, a name coincidentally derived from the initials of inventor Harold Caminez and sales manager Harkness Cram, marking the standardization of helical inserts for . Following , threaded inserts expanded beyond into broader industrial uses, including automotive and sectors, as demands grew for reliable fastening in mass-produced components. Key-locking variants, originally designed during the war for , evolved post-war to support lighter, more efficient assemblies in vehicles and electronic devices. The saw further evolution with inserts optimized for plastics, building on earlier applications but adapting to new thermoplastics through methods like ultrasonic insertion and heat staking, enabling stronger, reusable threads in and automotive interiors. Standardization efforts in the 1970s and 1980s formalized threaded insert specifications, with organizations like ASME and ISO developing guidelines for thread forms and tolerances; for instance, ISO R 1501 (1970) addressed miniature threads suitable for inserts, while ASME B1.1 updates in the 1980s refined unified inch screw threads for broader compatibility. In the 2000s, self-tapping threaded inserts gained prominence for composite materials, offering installation without pre-tapping and improved performance in lightweight structures like those in and automotive composites, with designs from manufacturers like Tappex emphasizing chip-free entry into fiber-reinforced polymers. As of 2025, threaded inserts continue to evolve with integration into , where heat-set and press-fit variants enhance durability in additively manufactured parts, particularly in renewable energy applications such as components, alongside sustainable material adaptations like recycled alloys to reduce environmental impact.

Types

Helical Inserts

Helical inserts, also known as wire thread inserts, consist of a precision-formed coil made from diamond-shaped wire, typically in materials such as , which creates internal threads through the edges of the wire when installed in a specially tapped with a 60° thread form. This helical spring-like structure distributes loads evenly across the parent material, minimizing stress concentrations and enabling effective use in repairing damaged threads or reinforcing thin materials. These inserts offer high resistance to and shock due to their flexible coil design, which absorbs dynamic loads and prevents loosening in demanding environments. They require minimal removal during installation, as the special STI ( Insert) tap is only slightly larger than the original hole, preserving the of the workpiece, and are particularly suited for thread repair in metals where original threads have been stripped or worn. Compared to solid inserts, helical designs provide a lighter weight alternative while maintaining comparable thread strength. Variants include standard free-running inserts with smooth threads for general applications, as well as coarse and fine pitch options available in UNC/UNF inch sizes or metric equivalents to match specific requirements. Locking features, such as screw-locking types with deformed coils or chords that grip the , enhance hold under ; additional options like Hi-Torque for lubricated high-load scenarios or stud-lock for rods further customize performance. Inserts come in tanged (with a drive tang for installation) and tangless configurations to reduce foreign object debris in sensitive assemblies. Installation involves drilling the hole to the specified size, countersinking the entrance, with an STI tool to create the helical groove, and then inserting the coil using a or prewinder tool, which expands the insert to lock it in place. For tanged variants, a unique step follows where the protruding tang is broken off and removed after insertion to ensure a flush, secure fit without interfering with the . This process can be performed manually or with pneumatic/electric tools for efficiency in production settings.

Solid Inserts

Solid threaded inserts feature fully solid metal or alloy bodies, typically constructed from steel, , , or aluminum, which provide internal threads for mating with fasteners while incorporating external features such as threads, knurls, or barbs for secure retention in the host material. These inserts differ from repair-oriented helical types by serving as primary, permanent fastening solutions in demanding applications. Key subtypes include externally threaded variants, which screw directly into a pre-tapped for robust engagement, and press-fit designs that rely on or barbs to lock into place without threading, suitable for installation via pressing, ultrasonics, or heat. Captive or self-retaining nuts represent another subtype, featuring a mechanism that deforms the surrounding material to anchor the insert permanently, often used in panels. These inserts offer superior compared to alternatives, with examples achieving pull-out resistances up to 61,360 pounds in phenolic materials, making them ideal for high-load scenarios in metals like aluminum and , as well as hard plastics. Their solid construction eliminates risks associated with unraveling components, ensuring long-term durability and resistance to without compromising thread integrity. Specific variants include flanged designs, which incorporate a wider head to distribute loads over a larger surface area and provide a bearing surface for added stability, versus flush types that install level with the surface for aesthetic or space-constrained applications. Self-tapping solid inserts, equipped with cutting edges or slots, form their own initial threads in the host material during installation, reducing the need for precise pre-drilling and enhancing efficiency in softer substrates like thermoplastics. Load distribution in solid inserts occurs through direct engagement of external threads or retention features with the base , enabling effective transmission and preventing rotation under stress, which supports higher clamping pressures—up to 50% greater than standard tapped holes.

Molded and Potted Inserts

Molded and potted inserts represent methods for integrating threaded fasteners directly into or composite materials during or shortly after the forming process, ensuring seamless encapsulation and enhanced load distribution. These inserts typically feature or bodies engineered with features like , undercuts, or flanges to promote mechanical interlocking and chemical bonding with the surrounding matrix. In mold-in variants, the inserts are positioned within the mold cavity using core pins or orientation jigs to maintain precise thread alignment before the cures, allowing the molten to flow around and encapsulate the insert fully during injection or . This encapsulation process creates a robust chemical and mechanical bond between the insert and the base material, providing superior resistance to pull-out and compared to post-molded installations, while eliminating the need for secondary assembly steps. Molded inserts are particularly advantageous for high-volume production in thermoplastics, where automated placement enables consistent integration across large batches. Specific variants include symmetrical or blind-ended designs suited for thermosets and filled plastics, as well as heat-staking mold-in types that leverage thermal deformation of thermoplastics to secure the insert during the molding cycle. Potted inserts, in contrast, involve inserting the into a pre-formed hole and filling the surrounding void with a such as to achieve encapsulation, making them suitable for irregular holes or repairs in composites. The potting compound is injected after excavating any core material if present, curing to form a strong bond that enhances overall strength in composite structures. -potted variants offer versatility for applications requiring post-insertion adjustment, providing reliable performance in softer substrates like plastics.

Materials and Design

Common Materials

Threaded inserts are commonly manufactured from metals such as , , , and aluminum, each selected for specific properties that ensure compatibility with various base materials and applications. offers excellent resistance, , and thermal conductivity, making it ideal for electrical, marine, and applications where it provides strong holding power without excessive wear on softer substrates. provides superior strength and rust resistance, particularly in A2 and A4 grades, suiting it for harsh, chemical-exposed, or high-load environments like marine or industrial settings. , often zinc-plated for added protection, delivers cost-effective durability for general-purpose uses in heavy-duty assemblies. Aluminum, being lightweight and recyclable, is favored in and automotive components where weight reduction is critical, though it requires careful handling to avoid thread stripping due to its relative softness. Polymer alternatives, such as inserts or those with polymer coatings, are used for vibration in dynamic applications, absorbing shocks and preventing loosening without the conductivity of metals. Material selection prioritizes compatibility with the base material, including matching coefficients to prevent issues like cracking in plastics— is often chosen for thermoplastics like ABS due to its similar expansion rate. Additionally, hardness differences between the insert and mating are considered to minimize . As of 2025, trends emphasize through lead-free alternatives like aluminum and advanced coatings such as zinc flake, supporting eco-friendly while maintaining performance. Material choices directly influence load-bearing capacity, with harder options like enhancing pull-out resistance in demanding scenarios.

Design Considerations

The design of threaded inserts begins with factors that ensure compatibility and in the host material. Thread pitch must match the intended bolt size to achieve proper seating , such as M5 x 0.8 or 10-32 configurations that align with standard dimensions. diameter plays a critical role in load distribution by providing an increased bearing surface, as seen in headed inserts where the flange spreads forces to prevent localized stress concentrations. Knurl patterns are selected based on the need for grip; straight knurls enhance torsional resistance, while helical knurls at 30-45° angles improve pull-out strength particularly in soft materials. Compatibility considerations focus on integration with the receiving hole and overall assembly reliability. Hole tolerances, such as H7 for press-fit applications, ensure precise insertion without excessive play or binding, with recommended hole depths at least the insert length plus two thread pitches to accommodate full engagement. Pull-out resistance is optimized through features like barb angles, which in designs such as hexagonal-barbed inserts provide mechanical interlocking, achieving forces up to 135 lbs in materials like ABS. Customization allows adaptation to specific needs. Oversized inserts compensate for in high-cycle applications by providing additional for repeated threading. Multi-thread starts facilitate quicker assembly by reducing the number of rotations needed for engagement. Adherence to established standards ensures and quality. Internal threads typically conform to ASME B1.1 (Unified Inch Screw Threads) for class 2B fits or ASME B1.13M (Metric Screw Threads) for 6H tolerances, promoting consistent performance across manufacturers. In softer metals, finer knurls can be incorporated to maximize grip without compromising integrity.

Performance Factors

Strength and Load-Bearing Capacity

Threaded inserts are engineered to provide robust mechanical performance under various loads, with axial pull-out force serving as a primary metric for tensile strength. This force quantifies the maximum axial load an insert can resist before extraction from the host material, typically governed by shear failure at the thread interface. The pull-out force FF is approximated by the formula F≈πdLτF \approx \pi d L \tau where dd is the mean diameter at the shear plane, LL is the length of engagement, and τ\tau is the ultimate shear strength of the weaker material (insert or parent), with a safety factor applied based on application demands. This calculation relies on the minimum shear engagement area multiplied by the allowable shear stress, ensuring the insert outperforms direct tapping in softer materials like aluminum. Torsional strength evaluates an insert's resistance to rotational loads, crucial for applications involving tightening or vibrational . Key factors influencing torsional performance include engagement , material properties, and thread geometry. Common failure in torsion occurs via thread stripping, where the exceeds the shear capacity of the threads. To approximate, the stripping can be estimated considering the shear area across engaged threads. Key factors influencing these strengths include engagement , with a minimum of 1.5 times the recommended for metallic parent materials to optimize load distribution and prevent premature stripping. Additionally, the standard 60° thread form in Unified systems promotes even stress distribution, enhancing overall torsional performance. Under cyclic loading, fatigue resistance becomes paramount, as repeated axial or torsional stresses can lead to progressive weakening. life is assessed through standards like ISO 3800, which outlines axial load to generate S-N curves for threaded fasteners, including inserts, under controlled cyclic conditions. For composite applications, ASTM D7332 specifies pull-through testing to measure resistance to bearing failure under multidirectional loads. Common failure modes include thread stripping—a shear-dominated extraction of the insert—or base material yield, where the parent deforms plastically; the latter is preferable as it allows for inspection and repair without total joint compromise. To illustrate engagement guidelines based on material strengths, the following table provides recommended minimum lengths in multiples of nominal diameter:
Parent Material Shear Strength (MPa)Screw Ultimate Strength (MPa): 3004005006008001000
701.522.53.5--
10011.51.522.53
150111.51.522
20011111.51.5
250111111.5
300111111.5
350111111.5

Environmental Resistance

Threaded inserts exhibit robust resistance through inherent material properties and applied coatings tailored to specific environments. In variants, passivation forms a passive layer on the surface, which self-heals in the presence of oxygen and provides protection against pitting and in atmospheric and aqueous conditions. inserts, prone to rusting, are commonly -plated to act as a sacrificial , delaying substrate ; chromate conversion coatings on further extend resistance, achieving up to 96 hours without white in neutral salt spray exposure. For heightened chemical aggression, (PTFE) coatings on inserts create a barrier, repelling acids, bases, and solvents while reducing and during installation. Temperature tolerance in threaded inserts is achieved via specialized alloys and composites that maintain integrity across wide thermal ranges. High-temperature applications employ nickel-based alloys like , which offer oxidation resistance up to 1000°C through stable phases and a protective scale, suitable for and furnace components. At the opposite extreme, low-temperature performance is enhanced in plastic matrices reinforced with glass fibers, such as nylon 6/6, where the filler improves tensile strength and minimizes embrittlement down to -40°C, ensuring reliable thread retention in cryogenic or outdoor settings. Chemical resistance is optimized by selecting superalloys like Hastelloy C-276 for inserts exposed to aggressive media, which demonstrates corrosion rates below 0.1 mm/year in (up to 20 wt% at boiling) and (up to 60 wt% at boiling), as well as moderate tolerance to oxidizing bases and chlorides. These material synergies—combining base alloys with coatings—extend service life in and marine contexts. Performance is rigorously evaluated using standards such as ASTM B117 for salt spray corrosion simulation, where qualified inserts endure 500-1000 hours without significant degradation, and MIL-STD-810 Method 503.7 for thermal cycling, verifying endurance through 10-50 cycles between -55°C and 125°C without cracking or loss of function. In extreme conditions, such resistance may indirectly influence load-bearing capacity by preventing material weakening from oxidation or embrittlement.

Installation Techniques

Mechanical Methods

Mechanical methods for installing threaded inserts rely on physical force to embed the insert into a pre-prepared , ensuring secure retention through , , or self-tapping action. These techniques are commonly used for metals, woods, and plastics, with variations depending on the insert type and substrate material. Proper hole preparation is essential, typically involving to specific diameters and depths as specified by the manufacturer to achieve optimal fit and performance. Press-fit installation involves forcing knurled or barbed inserts into pre-drilled holes using mechanical pressure, making it suitable for solid insert types in metals or hard materials. The process begins by aligning the insert's pilot end with the hole, followed by applying force with an arbor press, hydraulic tool, or even a hammer for smaller components. Automated pneumatic installers are employed for high-volume production to ensure consistent seating. Hole sizes are precisely matched to the insert's outer diameter, often requiring reaming for smooth insertion without distortion. Threaded installation, particularly for externally threaded or self-tapping variants, entails screwing the insert into a pre-drilled or lightly tapped to create mating threads in the substrate. A dedicated driver tool, such as a hand tapper or pneumatic installer, engages the insert's drive feature to rotate it while applying axial force, cutting or forming threads as it advances. The applied during installation should be as recommended by the manufacturer to secure the insert without stripping. sizes are selected per insert , often slightly smaller than the insert's major to allow thread engagement. Hand drivers suffice for low-volume work, while press attachments enable precise control in production settings. Ultrasonic installation uses high-frequency to embed inserts, primarily in , by generating frictional at the insert- interface for a fused bond. The insert is placed in a pre-drilled , and an ultrasonic horn applies downward pressure while vibrating at approximately 20 kHz, melting a thin layer of to flow around the insert's knurls or barbs for embedment. Tool kits include ultrasonic presses with size-specific horns and generators for controlled , , and dwell time. Hole preparation involves coring or to exact dimensions, with boss diameters ideally twice the insert diameter for enhanced strength. This method supports rapid, automated cycles in . Proper installation in subsequent use ensures the insert achieves its full load-bearing capacity.

Chemical and Thermal Methods

Chemical and thermal methods provide effective installation techniques for threaded inserts in non-metallic materials such as plastics, composites, and wood, relying on bonding through adhesives, resins, or heat rather than mechanical force. These approaches enhance load distribution and prevent loosening in applications where pressing is impractical or could damage the substrate. involves applying or anaerobic adhesives to the exterior of the insert before insertion into a prepared hole. adhesives, such as those thickened with fillers like , are wetted into an oversized (typically 2/3 to 3/4 of the insert depth and up to twice the diameter) to ensure penetration and filling of voids, providing strong mechanical interlocking upon curing. Full strength is achieved after a minimum cure time of 24 hours, though longer durations are recommended in cooler conditions to allow complete hardening. Anaerobic adhesives, such as retaining compounds, are suitable for metal substrates and cure in the absence of air when confined between close-fitting metal surfaces, forming a tough bond that resists . These are applied sparingly to the insert's knurled or smooth exterior and set within minutes to hours, depending on the formulation. Potting encapsulates the insert by filling surrounding voids with a resin such as or , creating a solid anchor particularly in composites or porous substrates. The process begins by drilling a to the insert and undercutting for at least 0.040 inches (1 mm) clearance around and below the insert to accommodate the compound. The potting compound is then injected through the insert's installation tab until it overflows, ensuring complete void filling; in composites, vacuum assistance removes air pockets for better resin flow and . The assembly cures per the resin specifications, often 24 hours or more, resulting in a flush, load-bearing installation. Thermal methods, such as hot-melt insertion, are ideal for thermoplastics where heat reflows the base material around the insert for a secure fit. or heat-set inserts are heated using an ultrasonic horn or tip, melting the surrounding plastic (e.g., in 3D-printed or parts) before cooling to form a fused bond; pilot holes should be sized according to manufacturer specifications, typically slightly smaller than the insert's outer to ensure proper fusion. This technique achieves rapid installation with high pull-out resistance in post-fabrication scenarios. Best practices for these methods emphasize surface preparation and material compatibility to maximize bond integrity. Substrates and inserts must be degreased with solvents like acetone and lightly abraded (e.g., 50-grit ) to remove contaminants and promote . Adhesives and resins should be selected based on compatibility charts matching the base material's chemistry and —epoxies for wood or plastics, anaerobics for metals—to avoid degradation or weak bonds. Excess material should be cleaned immediately, and full cure times observed before loading.

Applications and Alternatives

Common Applications

Threaded inserts find widespread use in applications, where they secure panels in fuselages and provide robust fastening for engine mounts, ensuring structural integrity under extreme conditions. In automotive contexts, these inserts are integral to interior components such as seat mountings, seat belts, steering wheels, and airbag assemblies, where they offer reliable anchoring in varied materials. Helical wire inserts, in particular, are favored in vibration-prone areas of both and automotive systems to maintain stability and prevent loosening during operation. In and consumer products, threaded inserts enable secure mounting within housings for appliances and devices, distributing loads effectively to avoid cracking in softer materials. Heat-set threaded inserts are commonly used during the manufacturing of 3D-printed prototypes, allowing for precise assembly of components in and prototyping applications. For furniture and , press-fit threaded inserts are employed in particleboard to enhance screw retention, particularly in cabinet construction where repeated assembly and disassembly demand durable threads in low-density materials. These inserts provide superior holding power in engineered woods like particleboard and MDF, supporting the assembly of modular furniture without compromising material integrity. As of 2025, emerging applications include threaded inserts in electric vehicle batteries, where they facilitate secure fastening in thermoplastic housings and composite structures to optimize assembly and vibration resistance. As of 2025, the global threaded inserts market is valued at approximately $385 million, driven by demand in automotive, electronics, and composites. In medical devices, these inserts are increasingly used with lightweight composites to create reliable joints in implantable and diagnostic equipment, prioritizing biocompatibility and strength in delicate assemblies. In high-load scenarios like aerospace, threaded inserts must withstand significant torque to meet performance demands.

Comparisons to Other Fasteners

Threaded inserts provide distinct advantages over self-tapping screws, particularly in applications requiring repeated assembly or use in softer materials like plastics and composites. Unlike self-tapping screws, which create threads by displacing material and are simpler to install without pre-drilling, threaded inserts offer reusable machine threads that resist stripping and maintain integrity over multiple cycles. This reusability stems from the insert's , which distributes loads more evenly across the threads, reducing stress concentrations and preventing the creep or deformation common with self-tapping screws in low-durometer materials. Self-tapping screws, while cost-effective for one-time or low-cycle uses, are prone to thread failure upon removal and reinsertion, limiting their suitability for high-maintenance scenarios. In comparison to rivnuts, which are blind threaded inserts ideal for single-sided access in sheet metal, general threaded inserts enable full through-threading for applications needing complete bolt passage and higher engagement length. Rivnuts excel in quick, blind installations but are limited to partial threading, potentially reducing overall holding power in thicker substrates. Threaded inserts often provide superior torque resistance due to their extended thread engagement and material reinforcement, making them preferable despite higher upfront costs for demanding torque applications. For instance, types like helical coil inserts can repair stripped self-tapping screw holes, offering a versatile alternative in maintenance contexts. Threaded inserts also outperform weld nuts in non-destructive installation processes, avoiding the heat-related issues inherent to . Weld nuts require fusion, which can cause , warping, or weakening in heat-sensitive materials like plastics, whereas inserts use mechanical or cold-forming methods to embed securely without introducing heat. This makes inserts environmentally friendlier, with no fumes, splatter, or energy-intensive equipment, and preserves the base material's integrity for cleaner assemblies. In plastics, weld nuts risk melting or altering material properties, while inserts maintain structural stability. Selection criteria for threaded inserts versus these alternatives often hinge on cost-benefit , favoring inserts in high-cycle or long-term applications where justifies the investment. In composites, inserts significantly extend by providing wear-resistant threads that withstand repeated loading without degradation, unlike self-tapping screws or weld nuts, which may fail prematurely under or reassembly. Lifecycle evaluations highlight reduced and replacement needs, positioning inserts as optimal for scenarios demanding reliability over initial simplicity.

References

  1. https://monroeengineering.com/blog/what-is-a-threaded-insert/
  2. https://press.biscoind.com/2016/01/13/what-is-a-threaded-insert/
  3. https://groov-pin.com/knowledge-base/faqs/threaded-inserts-faqs/threaded-insert-faqs/
  4. https://xometry.pro/en/articles/threaded-inserts-for-plastics/
  5. https://monroeaerospace.com/blog/what-are-the-different-types-of-threaded-inserts/
  6. https://uk.rs-online.com/web/content/discovery/ideas-and-advice/threaded-inserts-guide
  7. https://www.rapicoil.com/post/history-of-wire-thread-inserts
  8. https://www.dbroberts.com/threaded-inserts-and-insert-tools.html
  9. https://teampipeline.us/what-are-the-benefits-of-threaded-inserts/
  10. https://www.pemnet.com/products-overview/products-threaded-inserts/
  11. https://www.spirol.com/assets/files/ins-threaded-inserts-design-guide-us.pdf
  12. https://us.misumi-ec.com/blog/benefits-of-threaded-inserts/
  13. https://www.pemnet.com/wp-content/uploads/sites/2/2022/06/sidata.pdf
  14. https://fasteningandbonding.net/qa-helicoil-threaded-inserts
  15. https://www.emerald.com/insight/content/doi/10.1108/eb036165/full/pdf
  16. https://www.boeraneinsert.com/am/the-history-and-evolution-of-key-locking-inserts/
  17. https://www.model-engineer.co.uk/825/threaded-inserts-and-other-hot-topics/
  18. https://www.rebell-tools.de/en/Thread-Know-How/thread-standards.html
  19. https://www.wermac.org/societies/asme_part3.html
  20. https://www.tappex.co.uk/latest-blog-post-on-tappex-self-threading-thread-inserts-for-metal-plastics-composite-materials-and-wood/
  21. https://formlabs.com/blog/adding-screw-threads-3d-printed-parts/
  22. https://www.ezlok.com/why-you-should-use-threaded-inserts-for-3d-printing
  23. https://www.zeal3dprinting.com.au/top-5-emerging-3d-printing-materials-to-watch-in-2025/
  24. https://www.stanleyengineeredfastening.com/-/media/Web/SEF/Resources/Docs/Heli-Coil/HC-2000_rev11_web.pdf
  25. https://www.mfsupply.com/Helical-Inserts-aka-HeliCoil-Guide-FAQs-s/6322.htm
  26. https://www.ezlok.com/guide-to-helical-inserts-for-metal
  27. https://groov-pin.com/wp-content/uploads/2020/02/threaded_insert_brochure.pdf
  28. https://www.spirol.com/about-us/news/spirol-expands-press-in-insert-line-with-the-introduction-of-aluminum/
  29. https://www.ezlok.com/threaded-inserts
  30. https://www.ezlok.com/for-plastic/for-thermoset-plastic/ezpress-inserts-for-plastic
  31. https://www.pemnet.com/products-overview/products-nuts/nuts-clinch-nuts/
  32. https://www.ezlok.com/for-metal/ezlok-solid-wall-threaded-inserts
  33. https://www.ezlok.com/for-wood/for-soft-wood/ezhex-threaded-inserts-for-soft-wood
  34. https://www.pemnet.com/products/engineering-guides/si-threaded-inserts-for-plastic/
  35. https://www.ptonline.com/articles/four-ways-to-tackle-threaded-inserts-for-plastics
  36. https://www.yardleyinserts.com/product-tag/epoxied-in/
  37. https://www.abbottaerospace.com/aa-sb-001/12-joints/12-2-mechanically-fastened-joints/12-2-6-potted-inserts-in-cored-laminates/
  38. https://www.qewitfastener.com/blog/how-to-select-threaded-insert-materials-for-wood-plastic-and-metal/
  39. https://blog.componentsforindustry.com/choosing-the-perfect-threaded-insert-material/
  40. https://eppcomposites.com/nylon-pp-threaded-inserts-and-fasteners.html
  41. https://blog.katoadvanex.com/parent-material-requirements-for-wire-thread-inserts
  42. https://www.pemnet.com/wp-content/uploads/sites/2/2022/06/Thread_Galling.pdf
  43. https://www.rampa.com/eu/en/Online-Shop/Products/Inserts/
  44. https://engineeringlibrary.org/reference/loads-on-fastener-groups-nasa-design-manual
  45. https://www.stanleyengineeredfastening.com/-/media/web/sef/resources/docs/heli-coil/tensile_strength_hc68-2_rev4.pdf
  46. https://roymech.org/Useful_Tables/Screws/Thread_Calcs.html
  47. https://tameson.com/pages/thread-engagement-chart
  48. https://webstore.ansi.org/industry/fasteners/screws/screw-thread-inserts
  49. https://cdn.standards.iteh.ai/samples/9333/c51666a410f44d57aea3af13da089ca6/ISO-3800-1993.pdf
  50. https://roymech.org/Useful_Tables/Screws/Thread_inserts.html
  51. https://www-eng.lbl.gov/~shuman/NEXT/MATERIALS&COMPONENTS/Pressure_vessels/Atlas-Technical-Handbook-of-St-Steel-05-2008.pdf
  52. https://www.pemnet.com/resources/download-center/plating-guidelines/
  53. https://www.metcoat.com/pre-coated-fasteners.htm
  54. https://www.specialmetals.com/documents/nickel-alloy-handbook.pdf
  55. https://www.distrupol.com/Zytel_and_Minlon_Nylon_Resin_Molding_Guide_GNE-A11218-00-A1216_050117_OM.PDF
  56. https://haynesintl.com/wp-content/uploads/2024/08/c-276.pdf
  57. https://www.atec.army.mil/publications/Mil-Std-810G/Mil-Std-810G.pdf
  58. https://www.yardleyinserts.com/resources/technical-data/installation-methods/
  59. https://www.assemblymag.com/articles/91577-how-to-install-threaded-inserts
  60. https://www.pemnet.com/products-overview/products-threaded-inserts/threaded-inserts-ultrasonic-heat-staking-inserts/
  61. https://www.westsystem.com/instruction/epoxy-basics/bonding-fasteners-and-hardware/
  62. https://www.clarendonsf.com/products/inserts/potted-inserts
  63. https://www.padtinc.com/wp-content/uploads/2022/02/Best-Practice-Inserting-Hardware-Post-Build-EN.pdf
  64. https://rapidrivet.com/threaded-inserts-guide-knurled-hex-body-swaged-captive-inserts
  65. https://blog.componentsforindustry.com/what-are-threaded-inserts-used-for-in-the-automotive-industry/
  66. https://www.hfsindustrial.com/us/recoil
  67. https://egrove.olemiss.edu/cgi/viewcontent.cgi?article=2655&context=hon_thesis
  68. https://www.ezlok.com/for-wood
  69. https://www.yardleyinserts.com/product-tag/particleboard/
  70. https://www.tappex.co.uk/optimising-threaded-inserts-for-electric-vehicle-battery-systems/
  71. https://www.datainsightsmarket.com/reports/threaded-inserts-1512265
  72. https://www.linkedin.com/pulse/threaded-inserts-real-world-5-uses-youll-actually-see-9tg1f
  73. https://staubinc.com/news/when-to-use-threaded-inserts-for-machined-applications/
  74. https://blog.componentsforindustry.com/why-threaded-inserts-may-be-the-answer-for-your-injection-molding-application/
  75. https://blog.katoadvanex.com/drilling-and-tapping-vs.-wire-thread-insert-performance-which-is-best
  76. https://groov-pin.com/wp-content/uploads/2020/02/Threaded_Inserts_Benefits.pdf
  77. https://www.huyett.com/blog/rivet-nuts-and-rivet-nut-tools
  78. https://www.sherex.com/blog/rivet-nuts-vs-weld-nuts/
  79. https://www.pemnet.com/engineering-services/self-clinching-vs-welding/
Add your contribution
Related Hubs
User Avatar
No comments yet.