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Jam nut
Jam nut
Jam nut
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Standard nut employed as a jam nut against another standard nut

A jam nut is a low profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of locknut, where it is "jammed" up against a standard nut to lock the two in place. It is also used in situations where a standard nut would not fit.

The term "jam nut" can also refer to any nut that is used in the same function (even a standard nut used for the jamming purpose). Jam nuts, other types of locknuts, lock washers, and thread-locking fluid are ways to prevent vibration from loosening a bolted joint.

Use of two nuts to prevent self-loosening

[edit]

In normal use, a nut-and-bolt joint holds together because the bolt is under a constant tensile stress called the preload. The preload pulls the nut threads against the bolt threads, and the nut face against the bearing surface, with a constant force, so that the nut cannot rotate without overcoming the friction between these surfaces. If the joint is subjected to vibration, however, the preload increases and decreases with each cycle of movement. If the minimum preload during the vibration cycle is not enough to hold the nut firmly in contact with the bolt and the bearing surface, then the nut is likely to become loose.

Specialized locking nuts exist to prevent this problem, but sometimes it is sufficient to add a second nut. For this technique to be reliable, each nut must be tightened to the correct torque. The inner nut is tightened to about a quarter to a half of the torque of the outer nut. It is then held in place by a wrench while the outer nut is tightened on top using the full torque. This arrangement causes the two nuts to push against each other, creating a tensile stress in the short section of the bolt that lies between them. Even when the main joint is vibrated, the stress between the two nuts remains constant, thus holding the nut threads in constant contact with the bolt threads and preventing self-loosening. When the joint is assembled correctly, the outer nut bears the full tension of the joint. The inner nut functions merely to add a small additional force to the outer nut and does not need to be as strong, so a thin nut can be used.[1]

The jam nut essentially acts as the "other object", as the two nuts are tightened against each other. They can also be used to secure an item on a fastener without applying force to that object. This is achieved by first tightening one of the nuts onto the item. Then the other nut is screwed down on top of the first nut. The inner nut is then slackened back and tightened against the outer nut.

Jam nuts can also be used in situations where a threaded rod must be rotated. Since threaded rods have no bolt heads, it is difficult or impossible to apply torque to a threaded rod. A pair of jam nuts is used to create a point where a wrench may be used.

Jam nuts can be unreliable under significant loads. If the inner nut is torqued more than the outer nut, the outer nut may yield. If the outer nut is torqued more than the inner nut, the inner nut may loosen up.[2][1]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Jam nut

View on Grokipedia
from Grokipedia
A jam nut, also known as a thin nut or lock nut, is a low-profile, internally threaded typically hexagonal in shape and approximately half the height of a standard hex nut, designed to secure bolts or threaded rods by jamming against another nut or component to resist loosening from , , or mechanical stress. Jam nuts are commonly used in pairs: a full-height nut is first tightened to the desired position on the bolt, followed by the jam nut, which is then torqued against the primary nut to create a locking action through friction and deformation of the threads, preventing self-loosening in high-vibration environments such as , automotive, and industrial machinery applications. They can also be employed singly in confined spaces where a full nut would not fit, or to fasten components to softer materials like wood or plastic without causing damage. Available in various materials including low-carbon steel, , (such as 18-8 or 304 grade), , and silicon bronze to suit different environmental conditions like corrosion resistance or high strength, jam nuts adhere to standards such as ASME B18.2.2 for inch-series heavy hex jam nuts and DIN 439 for metric thin hex jam nuts, with thread sizes ranging from 1/4 inch to over 3 inches in diameter and thicknesses typically 0.5 to 0.75 times the nominal diameter. Their compact design offers advantages in space-constrained assemblies while providing reliable performance without additional locking mechanisms like adhesives, though they may require periodic retightening under extreme dynamic loads.

Introduction

Definition and Purpose

A jam nut is a low-profile, thin nut, typically about half the height of a standard hexagonal nut, designed to be tightened against another nut or component on a threaded to create and prevent loosening. This configuration jams the threads together, providing a mechanical lock that resists rotational movement. The primary purpose of a jam nut is to secure threaded fasteners in place under vibrational or dynamic loads, where standard nuts might otherwise back off due to transverse or axial forces. It achieves this by deforming the threads slightly or generating prevailing through the jamming action, which increases clamping force on the pressure flanks and minimizes relative motion between mating threads. This makes jam nuts particularly effective in applications involving machinery or equipment subject to ongoing vibration, without relying on additional adhesives or deformations. Jam nuts feature internal threads that match the specifications of the corresponding bolt, allowing them to engage securely, and an external hexagonal that enables wrenching for installation. Importantly, jam nuts are not self-locking on their own and must be used in conjunction with a primary nut or another component to fulfill their locking function.

Historical Context

The jam nut, a thin locking designed to secure against rotational loosening, emerged in the amid broader efforts to standardize nut and bolt production for industrial applications. This development was facilitated by advancements in machining technology, particularly Henry Maudslay's of the screw-cutting in 1800, which enabled the precise, interchangeable threading necessary for thin locking nuts to function reliably alongside standard nuts. Early references to jam-style nuts appear in U.S. patents for nut-locks, such as Aaron C. Vaughan's 1886 design (US349674A), which described a thin, spring-jawed nut applied tightly against a primary nut to create friction and prevent unintended turning on bolts. During the Industrial Revolution, jam nuts gained traction as a solution to self-loosening in high-vibration environments, particularly in infrastructure like railroads and bridges. Manufacturers such as Hoopes & Townsend produced railroad track bolts designed to prevent nuts from jarring off due to the vibrations from passing trains, maintaining secure fastening under dynamic loads. This adoption addressed critical safety concerns in expanding rail networks, where vibration-induced loosening could lead to structural failures, marking a key milestone in the evolution of reliable fastening systems. By the early , the growth of industrial machinery further propelled the use of jam nuts, as advancements in techniques allowed for their widespread availability and consistency. In the mid-, jam nuts continued to be used in various industrial applications.

Design and Specifications

Physical Structure

A jam nut consists of a hexagonal body characterized by six flat sides that enable secure engagement with a or socket tool for tightening. This structure provides a stable gripping surface while maintaining a compact profile. Internally, it features uniform threads that conform to the bolt's specifications, available in either coarse or thread series to ensure compatibility across standard sizes. The overall height is notably thin, typically ranging from 0.5 to 0.75 times the nominal bolt , distinguishing it from full-height nuts. Dimensional specifications adhere to standards such as ASME B18.2.2, where the width across flats matches that of a standard hex nut to allow use of the same tools, but with a significantly reduced thickness for space-constrained assemblies. For instance, in a 1/2-inch nominal size, the width across flats measures between 0.736 and 0.750 inches, while the thickness varies from 0.302 to 0.323 inches. Thread pitch aligns with the corresponding bolt series, ensuring full thread engagement without extension beyond the nut's height. Key structural elements include chamfered edges on both the top and bottom faces, which the corners to ease initial thread alignment and reduce the risk of cross-threading during installation. Jam nuts lack integrated prevailing features, such as deformed threads or inserts, relying instead on their positioning for functional performance. Unfinished jam nuts exhibit rougher bearing surfaces compared to machined finished variants, potentially influencing the consistency of thread engagement due to increased . When positioned adjacent to a full nut, the jam nut's thin profile allows it to lock the assembly by direct contact, preventing rotational movement.

Materials and Standards

Jam nuts are commonly manufactured from for general-purpose applications, where grades such as A, B, or C provide adequate strength and cost-effectiveness, often meeting specifications under ASTM A563 for and nuts. variants, including 18-8 (equivalent to AISI 304) and 316 grades, are preferred for environments requiring resistance, as outlined in ASTM F594 for nuts. For specialized uses, jam nuts comply with ASTM F467 to offer non-magnetic properties and moderate resistance, while nylon-insert jam nuts serve low-strength, vibration-resistant needs without materials. Key material properties emphasize durability, with carbon and alloy steels achieving high tensile strengths up to 120,000 psi in heat-treated forms to withstand operational stresses. Heat treatments such as and tempering are applied to enhance and prevent deformation, particularly for grades under ASTM A563, ensuring reliable performance in locking applications. Dimensional and threading standards for inch-series jam nuts are governed by ASME B18.2.2, which specifies hex and heavy hex jam nut configurations, while material specifications align with ASTM A563 for carbon/alloy steels and ASTM F594 for stainless. Metric equivalents follow ISO 4035 for thin chamfered hex nuts, with material properties per ISO 898-2 for mechanical requirements like proof loads. Jam nuts must undergo proof load testing as per these standards to verify they maintain locking integrity under specified axial loads without thread stripping or yielding.

Types and Variants

Hexagonal Jam Nuts

Hexagonal jam nuts represent the standard and most prevalent variant of jam nuts, featuring a six-sided polygonal that enables full 360-degree rotational adjustability using common tools. This design ensures compatibility with standard bolts and fittings, making it suitable for a wide range of general fastening applications where space constraints or locking mechanisms are required. They are typically produced to ASME B18.2.2 specifications, which define their dimensions including width across flats and thickness. These nuts are available in two primary subtypes: finished hexagonal jam nuts and heavy hexagonal jam nuts. Finished hexagonal jam nuts are precision-machined to achieve tighter tolerances, often Class 2B thread fit, and are employed in precision assemblies requiring accurate alignment and minimal play. In contrast, heavy hexagonal jam nuts feature thicker walls and a width across flats approximately 10% larger than standard finished types, providing a greater bearing surface area for distributing loads in high-torque scenarios. Both subtypes maintain a reduced thread engagement depth, generally about half that of full-height nuts, to facilitate their role in locking assemblies without excessive material overlap. The hexagonal form accounts for the majority of jam nut applications due to its versatility and alignment with conventional tooling, often used to lock against a standard nut in vibration-prone environments.

Specialized Forms

Specialized forms of jam nuts adapt the basic thin hexagonal design to meet niche requirements in fastening, often emphasizing ease of use, protection, or directional security over standard locking. These variants include slotted jam nuts, which feature radial slots across the top face to accommodate cotter pins or , enabling secure pinning in applications prone to . Such designs prevent unintended rotation by allowing the pin to pass through aligned holes in the mating bolt or stud. Left-hand thread jam nuts, with reverse threading that tightens counterclockwise, address counter-rotation scenarios in rotating assemblies, such as machinery or , where standard right-hand threads might loosen under operational . Wing jam nuts incorporate protruding wing-like extensions on the sides, facilitating hand-tightening without tools in frequent-adjustment setups, though they maintain the thin profile for jamming against primary nuts. Metric equivalents adhere to DIN 439 specifications, defining thin hexagonal jam nuts with a of approximately 0.5 times the nominal diameter for precise international applications. Acorn jam nuts blend a domed structure with internal threading, offering both a locking function—often enhanced by inserts per DIN 986—and a protective or aesthetic cover over exposed threads. These specialized forms prioritize targeted functionalities, such as electrical grounding in conductive materials like , where superior conductivity ensures reliable connections in electronic assemblies.

Applications and Uses

Industrial Applications

Jam nuts find extensive application in the automotive sector, where they secure suspension components to mitigate loosening from road-induced and dynamic loads. In construction, these fasteners are integral to framing, providing low-profile locking for bolted connections in high-load environments. The aerospace industry relies on jam nuts for engine mounts, where they maintain integrity amid extreme and thermal stresses. Jam nuts are used in the oil and gas sector for assemblies in demanding conditions. Marine applications leverage jam nuts for their compatibility with saltwater exposure, securing fittings on vessels and offshore structures against and wave-induced motion. In heavy machinery, such as excavators, jam nuts lock bearings in place to counter continuous operational vibrations and rotational forces. When paired with standard hex nuts, jam nuts enhance overall assembly reliability in these sectors by creating a dual-nut locking system.

Common Scenarios

Jam nuts are frequently employed in applications to secure eye bolts for load-bearing purposes, where they pair with the primary nut to prevent loosening under tension. For instance, mild steel eye bolts equipped with jam nuts support safe load ranges from 500 to 15,000 pounds in setups used for weighing and lifting operations. In bicycle maintenance, jam nuts lock adjuster nuts on components like handlebar stems, ensuring stable positioning and resistance to vibration-induced movement. This application leverages the nut's low-profile design to maintain adjustability without adding bulk to the assembly. Within factory settings, jam nuts facilitate the fastening and adjustment of conveyor systems, such as securing bearing holder plates on drive rollers or suspension rods for elevation control. These uses help maintain precise alignment and operational integrity in material handling equipment. A specific scenario involves HVAC systems, where jam nuts secure vibration isolators on compressor mounts using 1/2-inch threaded rods, helping to minimize transmission and equipment failure from operational . This setup supports minimum load capacities of 125 pounds per isolator while providing reliable . Jam nuts are often used in pairs on threaded rods to create adjustable shelving in warehouses, with one nut positioning the shelf and the second locking it in place to resist shifting under load. Their thin profile—typically half the height of a standard hex nut—allows multiple units to stack closely without excessive height buildup, making them suitable for space-constrained DIY furniture assembly projects.

Installation and Locking Mechanism

Step-by-Step Procedure

The installation of a jam nut requires careful attention to sequence and technique to ensure effective locking without compromising the assembly. Two methods are commonly used. In one approach, the primary nut, which bears the main load, is secured first to the specified value based on the bolt size, , and application standards. This step establishes the proper preload on the . Subsequently, the jam nut is threaded onto the bolt and positioned directly against the primary nut. To engage the locking mechanism, the jam nut is then tightened firmly against the primary nut to create mechanical interference through thread friction. Throughout this process, two wrenches are essential: one to counter-hold the primary nut and prevent or unloading, and the other to apply to the jam nut. An alternative method, recommended for optimal performance in high-vibration environments, places the jam nut first adjacent to the joint and tightens it to 25% to 50% of the full , followed by the primary nut tightened to the full specified while holding the jam nut stationary. Appropriate tools include open-end wrenches or socket wrenches matched to the across-flats of the nuts, along with a calibrated for the initial primary nut setting to achieve precise preload without exceeding material yield limits. For removal, the process is reversed by first loosening the jam nut to relieve the , followed by unscrewing the primary nut, which helps preserve thread integrity. Over-tightening the jam nut can cause , where metal from the threads binds and wears, significantly reducing reusability and potentially leading to joint failure. This friction-based locking provides effective prevailing without requiring specialized coatings or inserts.

Advantages Over Alternatives

Jam nuts offer significant economic benefits due to their low production and costs, typically under $0.50 per unit in standard steel configurations for common sizes such as 3/8-inch or M10, making them accessible for widespread industrial use. Their thin profile, often half the height of standard hex nuts, enables space-efficient installations in confined areas where full-height fasteners would be impractical, such as in machinery assemblies or adjustable mechanisms. As all-metal components with standard threads, jam nuts are highly reusable, incurring minimal thread damage during repeated installations and removals compared to deformed-thread locknuts, allowing for multiple cycles without compromising performance. In paired configurations, jam nuts deliver effective locking through frictional jamming of threads, which enhances resistance to vibration-induced loosening far beyond that of a single nut alone. Unlike methods requiring supplementary elements such as spring washers, jam nuts necessitate no additional components for locking, thereby reducing assembly time in high-volume production settings through simplified procedures. This inherent simplicity positions jam nuts as an ideal choice for high-volume manufacturing environments, where straightforward design and reliable performance outweigh the need for more complex locking technologies.

Comparisons and Limitations

Versus Other Locknuts

Jam nuts differ from nylon-insert locknuts primarily in their locking mechanism and environmental suitability. Unlike nylon-insert locknuts, which rely on a deformable insert to create friction and resist loosening, jam nuts provide a metal-to-metal contact through pairing with a standard nut, avoiding any non-metallic components that could degrade under . This all-metal design allows jam nuts to operate effectively at much higher temperatures, up to approximately 800°F depending on the material, compared to the 250°F limit of nylon-insert locknuts, making jam nuts preferable in high-heat applications such as engines or industrial machinery. In comparison to castellated nuts, jam nuts offer a simpler and more cost-effective solution for general resistance but lack the precision and security features suited for safety-critical applications. Castellated nuts feature slotted tops designed for cotter pins, which provide a mechanical lock that prevents rotation in high-stakes environments like or automotive suspension systems, ensuring precise alignment and tamper-proof fastening. Jam nuts, by contrast, do not accommodate cotter pins and rely solely on frictional jamming, which is less precise for such uses but reduces complexity and expense in non-critical setups. Jam nuts also contrast with prevailing torque locknuts in their installation and adaptability to constrained environments. Prevailing torque locknuts achieve self-locking through deformed threads or inserts that generate consistent resistance during tightening, allowing standalone use without a secondary . In tight spaces, however, jam nuts' thin profile—typically half the height of a standard nut—enables easier access and pairing against another nut for locking, whereas prevailing torque variants may require more clearance due to their locking features. A key distinction from wedge-lock washers lies in their respective focuses on adjustment and clamping. Jam nuts excel in scenarios requiring axial adjustments, such as in turnbuckles or leveling assemblies, where the paired nuts can be fine-tuned along the bolt's length to maintain position under load. Wedge-lock washers, however, prioritize radial clamping through their cam and design, which locks against rotational loosening via tension but offers limited utility for axial positioning.

Potential Drawbacks

Jam nuts can be reused multiple times, but repeated jamming may lead to thread galling, especially without lubrication, with sources suggesting up to 10 cycles for similar all-metal designs before performance may compromise. Thread galling occurs due to the high friction generated during installation of all-metal locking mechanisms, leading to material transfer and seizing between the nut and bolt threads. This deformation permanently alters the threads, reducing locking effectiveness and necessitating replacement after repeated use. Proper installation requires precise application to achieve the jamming effect without over-compression, as excessive can strip threads or cause bolt . Over-tightening increases the of thread , particularly in the thin nut's limited engagement area, potentially leading to joint failure under load. In applications involving high-cycle or repeated vibrations, jam nuts are not ideal without adequate , as unlubricated threads accelerate and reduce resistance to dynamic loosening. The thin profile of jam nuts, often half the height of standard nuts, results in shorter thread engagement, which can lower the overall clamp load capacity compared to full-height nuts in high-stress scenarios. Bare jam nuts are susceptible to in corrosive environments, accelerating degradation without protective coatings and compromising structural over time. variants are often required to mitigate this issue in harsh conditions. If the jam nut is not tightened sufficiently against the primary nut, it may fail to provide adequate locking, increasing the risk of self-loosening under and potentially leading to joint failure.

References

  1. https://monroeaerospace.com/blog/what-are-jam-nuts-and-how-do-they-work/
  2. https://www.albanycountyfasteners.com/blog/what-are-jam-nuts/
  3. https://boltport.com/products/jam-nuts/
  4. https://extreme-bolt.com/blog/what-is-a-jam-nut/
  5. https://www.mcmaster.com/products/jam-nuts/
  6. https://www.fastenermart.com/jam-nuts.html
  7. https://www.aspenfasteners.com/content/pdf/Metric_DIN_439_spec.pdf
  8. https://g-fast.com/understanding-finished-hex-jam-nuts-and-heavy-hex-nuts-key-differences-uses-and-advantages/
  9. https://www.portlandbolt.com/technical/faqs/hex-vs-heavy-hex-jam-nuts/
  10. https://www.boltscience.com/pages/twonuts.htm
  11. https://www.dysoncorp.com/blog/when-do-you-need-to-procure-a-jam-nut-vs-hex-nut/
  12. https://www.nord-lock.com/learnings/knowledge/2016/standards-the-search-for-a-red-thread/
  13. https://patents.google.com/patent/US349674A/en
  14. https://archive.org/details/HistoryOfTheBoltAndNutIndustry
  15. https://www.wipi.com/the-history-of-the-fastener
  16. https://www.aftfasteners.com/hex-jam-nuts-dimensions-technical-information/
  17. https://www.engineersedge.com/hex_nut.htm
  18. https://brass-neutral-links.com/product/brass-jam-nuts-brass-hex-hex-jam-nuts/
  19. https://www.ayafasteners.com/blog/what-is-the-surface-roughness-of-hex-nuts-1242632.html
  20. https://www.portlandbolt.com/products/nuts/heavy-hex-jam/
  21. https://www.fastenal.com/product/details/75147
  22. https://www.boltport.com/products/jam-nuts/
  23. https://www.engineersedge.com/hardware/metric_hex_jam_nuts__13732.htm
  24. https://www.portlandbolt.com/products/nuts/hex-jam/
  25. https://itafasteners.com/products-nuts-hex-jam.php
  26. https://www.mudgefasteners.com/news/2021/3/24/know-your-nuts-common-hex-nuts
  27. https://www.huyett.com/blog/lock-nuts
  28. https://www.huyett.com/all-products/nuts/lock-nuts/slotted-hex-nuts
  29. https://www.fmwfasteners.com/collections/slotted-hex-nuts
  30. https://www.uboltit.com/products/products_list/slotted-hex-nuts/
  31. https://www.mcmaster.com/products/jam-nuts/thread-direction~left-hand/
  32. https://www.sriperformance.com/HEX-JAM-NUTS-THIN-PATTERN-LEFT-HANDED
  33. https://www.dbroberts.com/wing-nuts.html
  34. https://belmetric.com/nuts/acorn-cap-nuts/
  35. https://accu-components.com/us/nylon-locking-dome-nuts/62157-HNDN-M4-A2
  36. https://www.amazon.com/Currie-Enterprises-Suspension-Parts-CUR-CE9114JN/dp/B086QGWZ6R
  37. https://www.nickel-systems.com/industries/fasteners-for-aerospace/
  38. https://teshifasteners.com/hex-jam-nuts/
  39. https://parts.southeasternequip.com/product/case-construction-jam-nut-425-1520/
  40. https://selletonscales.com/products/load-cell-eye-bolts-rice-lake
  41. https://bicycles.stackexchange.com/questions/12812/dahon-handle-post-hinge-loosens-too-quickly
  42. https://www.roachconveyors.com/manuals/sz_lsz_techbook.pdf
  43. https://morrisequipment.ca/wp-content/uploads/KSI-Conveyor-Maintenance-Training.pdf
  44. https://www.shareddocs.com/hvac/docs/2003/Public/04/cm12-om.pdf
  45. https://www.homedepot.com/p/Hillman-1-2-20-Stainless-Steel-Jam-Nut-8-Pack-43475/204775211
  46. https://www.instructables.com/Sliding-Shelves/
  47. https://maritime.org/doc/nstm/ch075.pdf
  48. https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf
  49. https://www.fastenersuperstore.com/products/208732/hex-jam-nuts
  50. https://accu-components.com/us/hex-jam-nuts/495691-HFN-M6-4-6-Z
  51. https://www.fastenal.com/products/details/37313
  52. https://www.faa.gov/sites/faa.gov/files/2023-08/AC_43.13-1B_Ch7.pdf
  53. https://www.fit-fastener.com/news/slotted-nuts-vs-castle-nuts-57.html
  54. https://csbn.copperstate.com/additional-resources/castle-nuts/
  55. https://aztechlocknut.com/understanding-different-locknuts/
  56. https://www.nord-lock.com/en-us/nord-lock/wedge-locking-technology/
  57. https://www.ndindustries.com/wp-content/uploads/MIL-DTL-18240F.pdf
  58. https://www.fastenermart.com/understanding-locking-fasteners.html
  59. https://www.velocitybolting.com/news/why-galling-occurs-on-threaded-fasteners
  60. https://www.nord-lock.com/learnings/bolting-tips/2017/prevent-bolt-galling-and-seizing/
  61. https://www.fastenerdata.co.uk/nut-fastener
  62. https://www.yitengfastener.com/blog/learn-about-the-advantages-of-using-hex-jam-nuts/
  63. https://www.wanhong-fastener.com/guide-to-fastener-anti-loosening/
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