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Metric gauge block set, 112 pcs
Another set with 8 pcs, 125 mm - 500 mm
Trolley model

Gauge blocks (also known as gage blocks, Johansson gauges, slip gauges, or Jo blocks) are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific thickness. Gauge blocks come in sets of blocks with a range of standard lengths. In use, the blocks are stacked to make up a desired length (or height).

Gauge blocks were invented in 1896 by Swedish machinist Carl Edvard Johansson.[1] They are used as a reference for the calibration of measuring equipment used in machine shops, such as micrometers, sine bars, calipers, and dial indicators (when used in an inspection role). Gauge blocks are the main means of length standardization used by industry.[1]

An important feature of gauge blocks is that they can be joined together with very little dimensional uncertainty. The blocks are joined by a sliding process called wringing, which causes their ultra-flat surfaces to cling together. A small number of gauge blocks can be used to create accurate lengths within a wide range. By using three blocks at a time taken from a set of 30 blocks, one may create any of the 1000 lengths from 3.000 to 3.999 mm in 0.001 mm steps (or .3000 to .3999 inches in 0.0001 inch steps).

Description

[edit]
How gauge blocks are measured.

A gauge block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart. Standard grade blocks are made of a hardened steel alloy, while calibration grade blocks are often made of tungsten carbide (WC), chromium carbide (CrC) or ceramic (SiO2-based) because they are harder and wear less.[2] Gauge blocks come in sets of blocks of various lengths, along with additional wear blocks, to allow a wide variety of standard lengths to be made up by stacking them. The length of each block is actually slightly shorter than the nominal length stamped on it, because the stamped length includes the length of one wring film, a film of lubricant which separates adjacent block faces in normal use. The thickness of the wring film is about 25 nanometers (0.98 μin).[3] The gauge's nominal length is also known as the interferometric length.[4]

In use, the blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and wrung together to form a stack of the required dimension. Gauge blocks are calibrated to be accurate at 20 °C (68 °F) and should be kept at this temperature when taking measurements. This mitigates the effects of thermal expansion. The wear blocks, made of a harder substance like tungsten carbide, are included at each end of the stack, whenever possible, to protect the gauge blocks from being damaged in use.

Machinists and toolmakers try to use a stack with the fewest blocks to avoid accumulation of size errors. For example, a stack totaling .638 that is composed of two blocks (a .500 block wrung to a .138 block) is preferable to a stack also totaling .638 that is composed of four blocks (such as a .200, .149, .151, and .138 all wrung together). Each block has a size tolerance of a few millionths of an inch, so stacking them together introduces a cumulative uncertainty (as detailed in § Grades below). However, the stacked error from even multiple blocks is usually negligible in all but the most demanding uses. In a busy shop, some of the blocks will be in use elsewhere, so one creates a stack from the blocks available at the time. Typically the few millionths of an inch difference will not be detectable, or matter, in the context. Contexts demanding ultimate precision are rarer and require additional expense (for example, more sets of blocks and higher grades of blocks).

Wringing

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See also: Optical contact bonding

Wringing is the process of sliding two blocks together so that their faces bond. Because of their ultraflat surfaces, when wrung, gauge blocks adhere to each other tightly. Properly wrung blocks may withstand a 300 N (67 lbf) pull.[5] The mechanism is a combination of:[4][5][needs update]

  • Vacuum applies pressure between the blocks because the air is squeezed out of the joint[note 1]
  • Surface tension from oil and water vapor that is present between the blocks
  • Molecular attraction that occurs when two very flat surfaces are brought into contact; this force causes gauge blocks to adhere even without surface lubricants, and in a vacuum
36 Johansson gauge blocks wrung together easily support their own weight.

It is believed that the last two sources are the most significant.[4] Experiments with friction of the blocks suggest also that the removal of the oxide film from the steel surface by wringing plays an important role in the wringing action.[7]

There is no magnetism involved, although to a user the clinging together of the blocks feels a bit like weak refrigerator magnets sticking together. Unlike magnets, however, the cling only lasts while the blocks are completely joined—the blocks do not attract each other across any visible gap, as magnets would.

The process of wringing involves four steps:[4]

  1. Wiping a clean gauge block across an oiled pad.
  2. Wiping any extra oil off the gauge block using a dry pad.
  3. The block is then slid perpendicularly across the other block while applying moderate pressure until they form a cruciform.
  4. Finally, the block is rotated until it is inline with the other block.

After use, the blocks are re-oiled or greased to protect against corrosion. The ability of a given gauge block to wring is called wringability; it is officially defined as "the ability of two surfaces to adhere tightly to each other in the absence of external means." The minimum conditions for wringability are a surface finish of 1 microinch (0.025 μm) AA or better, and a flatness of at least 5 μin (0.13 μm).[4]

There is a formal test to measure wringability. First, the block is prepared for wringing using the standard process. The block is then slid across a 2 in (51 mm) reference grade (1 μin [0.025 μm] flatness) quartz optical flat while applying moderate pressure. Then, the bottom of the gauge block is observed (through the optical flat) for oil or color. For Federal Grades 0.5, 1, and 2 and ISO grades K, 00, and 0 no oil or color should be visible under the gauge block. For Federal Grade 3 and ISO grades 1 and 2, no more than 20% of the surface area should show oil or color. This test is hard to perform on gauge blocks thinner than 0.1 in (2.5 mm) because they tend not to be flat in the relaxed state.[4]

Accessories

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A gauge block accessory set
A holder that turns a stack of gauge blocks into an instant, custom caliper or go/no go gauge.

The pictured accessories provide a set of holders and tools to extend the usefulness of the gauge block set. They provide a means of securely clamping large stacks together, along with reference points, scribers, and various shapes of blocks that act like caliper jaws, either external or internal. Conical-tip ones ease measurement of center-to-center distances between hole centers. A stack of gauge blocks with external caliper-jaw accessories, all clamped together, acts as a quickly assembled custom-size go or no-go gauge.

A special gauge block stone that cannot damage the surface is used to remove nicks and burrs to maintain wringability.[4]

There are two wringing pads used to prepare a gauge block for wringing. The first is an oil pad, which applies a light layer of oil to the block. The second is a dry pad, which removes any excess oil from the block after the oil pad has been used.[4]

Grades

[edit]
Gauge blocks (left in each picture, under optical flat) being used to measure the height of a ball bearing and a plug gage using interferometry. The interference fringes (lines) visible on the surface of the flats indicates error; the number of lines indicates the amount.

Gauge blocks are available in various grades, depending on their intended use.[8] The grading criterion is tightness of tolerance on their sizes; thus higher grades are made to tighter tolerances and have higher accuracy and precision. Various grading standards include: JIS B 7506-1997 (Japan)/DIN 861-1980 (Germany), ASME (US), BS 4311: Part 1: 1993 (UK). Tolerances will vary within the same grade as the thickness of the material increases.

  • reference (AAA): small tolerance (±0.05 μm or ±1.97 μin) used to establish standards
  • calibration (AA): (tolerance +0.10 to −0.05 μm or +3.94 to −1.97 μin) used to calibrate inspection blocks and very high precision gauging
  • inspection (A): (tolerance +0.15 to −0.05 μm or +5.91 to −1.97 μin) used as toolroom standards for setting other gauging tools
  • workshop (B): large tolerance (tolerance +0.25 to −0.15 μm or +9.84 to −5.91 μin) used as shop standards for precision measurement

More recent grade designations include (US Federal Specification GGG-G-15C):

  • 0.5 – generally equivalent to grade AAA
  • 1 – generally equivalent to grade AA
  • 2 – generally equivalent to grade A+
  • 3 – compromise grade between A and B

and ANSI/ASME B89.1.9M, which defines both absolute deviations from nominal dimensions and parallelism limits as criteria for grade determination. Generally, grades are equivalent to former US Federal grades as follows:

  • 00 – generally equivalent to grade 1 (most exacting flatness and accuracy requirements)
  • 0 – generally equivalent to grade 2
  • AS-1 – generally equivalent to grade 3 (reportedly stands for American Standard - 1)
  • AS-2 – generally less accurate than grade 3
  • K – generally equivalent to grade 00 flatness (parallelism) with grade AS-1 accuracy

The ANSI/ASME standard follows a similar philosophy as set forth in ISO 3650. See the NIST reference below for more detailed information on tolerances for each grade and block size. Also consult page E-4 of: Commercial Gauge Block Tolerances (Length refers to the calibrated thickness)

Manufacture

[edit]

Gauge blocks are usually made either from hardened alloy tool steels, ceramics or cemented carbides (such as tungsten carbide or tantalum carbide). Often the carbide has a hardness of 1500 Vickers hardness. Long series blocks are made from high-quality steel having cross section (35 × 9 mm) with holes for clamping two slips together. These are also available in carbon steel material. Steel blocks are hardened and tempered. The hardness is important because it slows down the gauge's rate of wear during use (this is why other kinds of gauges, such as pins, thread plugs, and rings, are also hardened.) The cutting of the blocks to size is accomplished with grinding followed by lapping. Usually no plating or other coating is involved. Blocks are kept very lightly oiled, and are stored and used in dry climate-controlled conditions; unplated, uncoated steel gauge blocks can last for decades without rusting.

History

[edit]

The gauge block set, also known as "Jo Blocks", was developed by the Swedish inventor Carl Edvard Johansson.[9] Johansson was employed in 1888 as an armourer inspector by the state arsenal Carl Gustafs stads Gevärsfaktori (Rifle Factory of Carl Gustaf's town) in the town of Eskilstuna, Sweden. He was concerned with the expensive tools for measuring parts for the Remington rifles then in production under licence at Carl Gustaf. When Sweden adopted a tailored variant of the Mauser carbine in 1894, Johansson was very excited about the chance to study Mauser's methods of measuring, in preparation for production under license at Carl Gustaf (which began several years later). However, a visit to the Mauser factory in Oberndorf am Neckar, Germany, turned out to be a disappointment. On the train home, he thought about the problem, and he came up with the idea of a set of blocks that could be combined to make up any measure.

There had already been a long history of increasing use of gauges up to this time, such as gauges for filing and go/no go gauges, which were custom-made individually in a toolroom for use on the shop floor; but there had never been super-precision gauge blocks that could be wrung together to make up different lengths, as Johansson now envisioned.

Back home, Johansson converted his wife's Singer sewing machine to a grinding and lapping machine. He preferred to carry out this precision work at home, as the grinding machines at the rifle factory were not good enough. His wife, Margareta, helped him with the initial prototyping. Once Johansson had demonstrated his set at Carl Gustaf, his employer provided time and resources for him to develop the idea. Johansson was granted his first Swedish patent on 2 May 1901, SE patent No. 17017, called "Gauge Block Sets for Precision Measurement". Johansson formed the Swedish company CE Johansson AB (also known as 'CEJ') on 16 March 1917.

Johansson spent many years in America; during his life he crossed the Atlantic 22 times.[citation needed] The first CEJ gauge block set in America was sold to Henry M. Leland at the Cadillac Automobile Company around 1908. The first manufacturing plant in America for his gauge block sets was established in Poughkeepsie, Dutchess County, New York, in 1919. The economic environment of the post–World War I recession and depression of 1920–21 did not turn out so well for the company, so in 1923 he wrote a letter to Henry Ford of the Ford Motor Company, where he proposed a cooperation in order to save his company. Henry Ford became interested, and on 18 November 1923 he began working for Henry Ford in Dearborn, Michigan. Hounshell (1984), citing Althin (1948) and various archive primary sources, says, "Henry Ford purchased the famous gaugemaking operation of the Swede C. E. Johansson in 1923 and soon moved it into the laboratory facility in Dearborn. Between 1923 and 1927, the Johansson division supplied 'Jo-blocks' to the Ford toolroom and any manufacturer who could afford them. It also made some of the Ford 'go' and 'no-go' gauges used in production as well as other precision production devices."[10]

In the early 20th century, the US inch was effectively defined as 25.4000508 mm (with a reference temperature of 68 °F [20 °C]) and the UK inch at 25.399977 mm (with a reference temperature of 62 °F [17 °C]).[11] When Johansson started manufacturing gauge blocks in inch sizes in 1912, Johansson's compromise was to manufacture gauge blocks with a nominal size of 25.4 mm, with a reference temperature of 20 °C (68 °F), accurate to within a few parts per million of both official definitions. Because Johansson's blocks were so popular, his blocks became the de facto standard for manufacturers internationally,[11][12] with other manufacturers of gauge blocks following Johansson's definition by producing blocks designed to be equivalent to his.[13]

In 1930, the British Standards Institution adopted an inch of exactly 25.4 mm. The American Standards Association followed suit in 1933. By 1935, industry in 16 countries had adopted the "industrial inch" as it came to be known,[14][15] effectively endorsing Johansson's pragmatic choice of conversion ratio.[11]

Co-branding of CEJ, Ford, and B&S logos.

In 1936, at the age of 72, Johansson felt it was time to retire and go back to Sweden. He was awarded the large gold medal of the Royal Swedish Academy of Engineering Sciences in 1943, shortly after his death.

In 1948 Brown & Sharpe bought the rights to the C. E. Johansson brand from Ford Motor Co.,[16] and blocks co-branded with the C. E. Johansson and Brown & Sharpe logos were made. Blocks co-branded with the C. E. Johansson and Ford logos are also sometimes still seen in use today.

Gauge pins

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Similar to gauge blocks, these are precision-ground cylindrical bars, for use as plug gauges to measure hole diameters, or as parts of go/no go gauges or similar applications.

Gauge rollers and balls

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These are supplied as sets of individual rollers or balls as used in roller or ball bearings or tool and die making applications. Calibration balls can be used to calibrate contact angle goniometers, CNC machines and similar equipment.

See also

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  • Optical flat – Extremely flat piece of optical-grade glass
  • Cold welding – Welding process in which joining occurs without melting or heating the interface
  • Optical contact bonding – Process whereby two closely conformal surfaces are held together by intermolecular forces.

Notes

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References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Gauge block

View on Grokipedia
from Grokipedia
A gauge block, also known as a gage block or Johansson block, is a precision-engineered rectangular or square used as a for length measurement in dimensional . It features two opposing flat, parallel measuring faces that are ground and lapped to high tolerances, allowing multiple blocks to be "wrung" together—adhered via molecular attraction and a thin lubricating of about 10 nm—to form arbitrary lengths up to 1 meter without gaps or corrections. The length of a gauge block is defined as the perpendicular distance from a gauging point on one face to an auxiliary plane wrung to the opposite face, including the wringing film thickness. Invented in 1896 by Swedish machinist and inventor Carl Edvard Johansson to standardize measurements in machine shops, gauge blocks revolutionized precision manufacturing by providing a reliable transfer standard traceable to the meter. Johansson received a for his design in 1901 (Swedish patent No. 17017) and established production in 1911, with early sets hand-finished using rudimentary tools like sewing machines for lapping. By the early , they were adopted globally; in the United States, the National Bureau of Standards (now NIST) began manufacturing equivalents in 1917 following William Hoke's innovations in block design. Over a century later, gauge blocks remain foundational despite advances in laser interferometry, serving for calibrating micrometers, , and coordinate measuring machines. Typically constructed from hardened (such as 52100) for durability and machinability, gauge blocks are also produced in for wear resistance, chromium carbide for low , and ceramics like zirconia for high stability in varying environments. Their , parallelism, and dimensional accuracy are governed by international standards, notably ISO 3650 (1998), which specifies rectangular blocks with nominal lengths from 0.5 mm to 500 mm in metric sets and defines accuracy grades K (calibration), 0, 1, and 2—based on maximum deviations from nominal length, such as approximately 0.07 μm for grade K at 100 mm. Calibration at institutions like NIST involves interferometric methods using stabilized lasers to achieve uncertainties as low as 20 nm, ensuring traceability to the SI meter definition.

Fundamentals

Definition and Purpose

Gauge blocks are precision-ground and lapped length standards consisting of metal or blocks with rectangular, square, or circular cross-sections and two flat, parallel opposing faces. These blocks are designed for high accuracy, with individual thicknesses typically ranging from 0.5 mm to 500 mm. The primary purposes of gauge blocks are to calibrate and set up precision measuring instruments, such as micrometers and ; to enable direct length measurements by combining multiple blocks; and to serve as master standards for in . They provide a reliable transfer standard for length , ensuring consistency in dimensional across industrial applications. Gauge blocks allow users to construct arbitrary by stacking them, adhering face-to-face through the wringing process to minimize gaps. For instance, a required of 45.6785 mm can be achieved using a combination of 25 mm, 17.5 mm, 1.17 mm, 1.008 mm, and 1.0005 mm blocks from a standard metric set.

Physical Characteristics

Gauge blocks are precision-engineered rectangular prisms with nominal typically ranging from 1 mm to 100 mm in standard sets, though individual blocks or extended sets can reach up to 1000 mm to accommodate broader metrological needs. The cross-section dimensions are standardized to ensure stability and handling ease, commonly measuring 9 mm in width by 12 mm in height for blocks up to 100 mm, with slight variations such as 30 mm × 9 mm for longer or specialized configurations to maintain proportional strength. The measuring faces, located at the two opposite ends of the block, are precision-ground and lapped to achieve exceptional geometric accuracy, with deviations from flatness and parallelism limited to 0.05 μm for high-grade blocks (such as Grade 00) up to 10 mm in length. These faces must also exhibit a fine surface texture, with arithmetic average roughness (Ra) typically less than 0.02 μm, enabling the molecular adhesion essential for their use in length standards. Markings, including the nominal length (in characters at least 1.5 mm high), manufacturer identification, and serial number for calibration-grade blocks, are engraved on the measuring faces while preserving a central unmarked area of at least 9 mm × 12 mm to avoid compromising precision. Key material properties contribute to the blocks' reliability as length standards. For steel gauge blocks, surface hardness is specified at a minimum of 800 HV (equivalent to approximately 60-65 HRC), providing resistance to deformation and low rates during handling and . The coefficient of linear for is (11.5 ± 1.0) × 10^{-6} /°C over the 10–30 °C range, ensuring dimensional stability under typical laboratory conditions. These attributes, combined with the use of wear-resistant materials, allow gauge blocks to maintain accuracy over extended periods with minimal degradation.

Usage

Wringing Process

The wringing process in gauge blocks relies primarily on surface tension from a thin liquid film and molecular attraction forces, such as van der Waals interactions, between the ultra-flat measuring faces, resulting in a near-zero gap that allows blocks to adhere without mechanical fasteners. When clean blocks are pressed together, the intervening oil film, typically around 25 nm thick, creates an airtight seal enhanced by air pressure and capillary effects, enabling the combined length to approximate the sum of individual block lengths with minimal addition from the wringing layer. This adhesion arises from the blocks' low surface roughness, often below 25 nm, and high flatness, which facilitate intimate contact over the entire face area. To perform wringing, first clean the measuring faces thoroughly using a lint-free cloth and solvent like alcohol or kerosene to remove contaminants, followed by a light wipe with a dry pad to ensure no residue remains. Next, apply a very thin coat of specialized gauge block oil to one face if needed for lubrication, then align the blocks on a flat, clean surface with faces slightly overlapping at a shallow angle of about 5-10 degrees. Slide the blocks together smoothly while applying gentle, even pressure to expel any trapped air or excess oil, rotating one block slightly if necessary to achieve full contact; the process should result in a total thickness increase of less than 0.2 μm per wringing interface due to the compressed film. Test the adhesion by attempting to lift the top block—it should cling firmly without visible gaps. Several factors influence the effectiveness of wringing, including surface , which must be free of or oils to prevent weak bonds; flatness, ideally better than 0.127 μm (5 microinches) to avoid air pockets; and compatibility, with steel blocks often providing more consistent results than ceramics due to differences in . The adhesion force can reach up to 300 across a typical face area of about 3 cm², equivalent to a pressure of roughly 100 /cm², sufficient to support stacked assemblies but dependent on these surface conditions. Despite its precision, wringing adhesion is temporary, lasting from hours to days depending on environmental and handling, and it is unsuitable for high-vibration settings where external forces could dislodge blocks. Repeated wringing can gradually wear surfaces if not done cleanly, potentially degrading flatness over time, though proper minimizes this.

Accessories and Applications

Gauge blocks are often used in conjunction with specialized accessories to facilitate precise alignment, protection, and maintenance during handling and storage. Wringing fixtures, such as holders and tie rods, aid in the stable stacking of blocks by providing alignment and securing mechanisms, particularly for square or long gauge blocks. Protective cases, typically fitted wooden enclosures, safeguard blocks from environmental contaminants and physical damage when not in use. Cleaning kits, including tools like Cerlube oil, optical flats, , blower brushes, and lint-free cleaning paper, enable thorough removal of burrs, contaminants, and residues to preserve surface flatness. Holders designed for , such as base stands and jaw attachments, position blocks accurately for verifying instrument accuracy across various lengths. In practical applications, gauge blocks serve as reference standards for calibrating coordinate measuring machines (CMMs), where check masters ensure table movement precision within micrometer tolerances. They are employed to verify thread gauges by providing exact pitch references, supporting in processes. For measurement, gauge blocks are stacked under sine bars to create precise elevations, enabling accurate trigonometric setups. In automotive and , workshop-grade blocks calibrate fixtures and instruments, ensuring component tolerances meet stringent safety standards. Modern implementations integrate gauge blocks with digital readouts, such as height masters offering 0.001 resolution, for rapid, user-friendly length verification. interferometers pair with blocks to achieve traceable measurements, using HeNe wavelengths for sub-micrometer accuracy in chains. These tools play a critical role in ISO 17025 accredited laboratories, where blocks underpin accreditation for dimensional services. Proper safety and maintenance practices are essential to prevent degradation. Blocks should be handled with cotton gloves or rubber-tipped to avoid scratches and thermal disturbances from skin contact. Storage at 20°C minimizes errors, with blocks kept in protective cases coated in preservatives if exceeds 50% to inhibit .

Standards and Grades

Classification System

Gauge blocks are classified into grades based on their precision and intended application, as defined by international and national standards such as ISO 3650 and ASME B89.1.9. The ISO 3650:1998 standard (confirmed 2025) specifies grades K (), 0, 1, and 2 for metric gauge blocks, where grade K represents the highest precision level suitable for and standards. In contrast, ASME B89.1.9-2002 (revised 2023) for inch and metric blocks uses grades K, 00, 0, AS-1, and AS-2, with grade AS-2 serving as the workshop or general-purpose grade for shop floor use. These classifications ensure and reliability in length measurement across different environments, from controlled labs to industrial settings. The 2023 ASME revision enhances specifications for accessories and metrological characteristics while maintaining core grades. The key differences among grades lie in their tolerance limits and suitability for specific tasks. Grade K (ISO) or 00 (ASME) blocks, used for calibrating other standards, have extremely tight tolerances minimizing deviations in high-precision applications. Grade 0 blocks, intended for and secondary standards, offer suitable tolerances, while grade 1 (or AS-1) provides tolerances for routine work. Grade 2 (or AS-2), the workshop grade, accommodates practical tolerances for direct gauging and setting tools in without requiring ultra-controlled conditions. Gauge block sets are typically composed to cover a range of lengths efficiently through wringing combinations, with the classic Johansson set serving as a representative example. A standard 112-piece metric Johansson set includes blocks from 1.0005 mm to 100 mm, featuring increments such as nine 1.001-1.009 mm blocks (0.001 mm steps), 49 blocks from 1.01-1.49 mm (0.01 mm steps), and larger steps up to 100 mm, available in both metric and inch variants to suit diverse needs. These sets enable the construction of any length within the range in 0.001 mm increments, optimizing utility for and . International variations in classification reflect evolving practices, with ISO 3650:1998 incorporating provisions for gauge blocks to enhance durability and thermal stability.

Tolerances and Specifications

Gauge block tolerances define the permissible deviations in , form, and other metrological properties to ensure their reliability as standards. The primary tolerance for deviation, known as the limit deviation, follows specifications in ISO 3650:1998, with values tabulated by grade and range; for example, for grade K blocks with nominal lengths 50-100 mm, the limit deviation is 0.07 μm. These values align with international standards for calibration-grade blocks used in precision . Form tolerances, including parallelism and flatness of the measuring faces, are critical to maintain accurate wringing and stacking. For grade blocks with nominal lengths up to 100 mm, both parallelism and flatness must not exceed specified limits, typically around 0.25 μm, preventing any significant variation in length across the surface during use. Additionally, the wringing film thickness—approximately 25 nm—formed between surfaces ensures additive lengths remain predictable within the tolerance band. These specifications apply across grades but tighten for higher precision classes like , as outlined in established metrological frameworks. Certification of gauge blocks requires traceability to the (SI) through optical , where the length is measured directly against the of in , typically using helium-neon lasers for sub-micrometer accuracy. This calibrates master blocks at national institutes, with commercial blocks then verified against them via methods, achieving repeat measurement uncertainties below 0.1 μm for lengths up to 500 mm. Environmental standardization is essential, with all specifications referenced to a temperature of 20°C under controlled conditions; deviations from this can introduce errors based on the block's coefficient of (typically 11.5 × 10^{-6}/°C for ). control between 40% and 60% is recommended to minimize effects on surface films and dimensional stability.

Manufacturing

Materials Selection

Gauge blocks are primarily manufactured from four types of materials: , , chrome carbide, and , each selected for their distinct mechanical and thermal properties that support high-precision dimensional measurement. , often high-carbon high-chrome , is the most common due to its affordability and ease of machining, though it is susceptible to and . offers superior hardness and wear resistance, approximately 10 times that of , making it ideal for demanding environments. Chrome carbide provides low similar to two-thirds that of , with high and stability. materials, typically based on zirconia, provide exceptional and resistance to cracking under normal use. A comparison of key properties highlights the trade-offs among these materials:
PropertySteelTungsten CarbideChrome CarbideCeramic (Zirconia)
Thermal Expansion Coefficient (×10^{-6}/°C)11.54.238.49.7
Hardness (HV)~800-9001450-1500~1500~1350
Wear ResistanceBaseline10× 10× 10×
MagneticYesNoNoNo
Corrosion ResistanceProne to HighHighExcellent
Thermal StabilityModerate (up to ~200°C)High (stable to 800°C)HighExcellent (low drift)
These properties derive from the inherent composition: steel's iron base enables magnetism but limits environmental durability, tungsten carbide's and chrome carbide's composite structures enhance stability and density similar to steel, and zirconia's glassy-ceramic nature ensures non-magnetic behavior and longevity exceeding 10 years in corrosive settings. Material selection depends on the application environment, required versus , and compatibility with the wringing . In cleanrooms or magnetic-sensitive setups, non-magnetic ceramics, carbides, or chrome carbides are preferred to avoid or interference, as steel's can attract iron particles. For high-wear or elevated-temperature applications, such as in automotive or up to 800°C, tungsten carbide's thermal stability and hardness justify its higher , offering extended service life over steel's typical 3 years. Wringing compatibility favors ceramics, chrome carbides, and tungsten carbides due to their superior surface finishes, which enable tighter adhesion and more accurate stacking without slippage, whereas steel requires meticulous cleaning to prevent oxidation-induced gaps. Overall, steel suits general use where budget constraints dominate, while advanced materials excel in precision labs balancing with performance demands.

Production Techniques

The production of gauge blocks involves a sequence of precise fabrication steps to achieve the required dimensional accuracy and surface . It begins with blank cutting, where bars or sheets are sectioned into approximate block shapes using methods such as band sawing for or jetting for other alloys. This is followed by rough grinding on surface grinders to remove excess material, establish initial parallelism, and prepare the blocks for further processing, typically reducing thickness by 0.005 to 0.010 inches per side. then stabilizes the blocks by austenitizing, , and annealing to relieve internal stresses and achieve consistent , often performed in furnaces to minimize . Precision refines the measuring faces to the final specifications, and the process concludes with comprehensive measurements to confirm , flatness, and parallelism. Key techniques emphasize high-precision material removal and surface conditioning. Rough and finish grinding utilizes automated horizontal spindle machines to maintain parallelism, ensuring deviations remain minimal throughout of up to 120 blocks. employs abrasives embedded in slurries or pads, rubbed against or tin-lead plates under controlled pressure, to generate extremely smooth surfaces with roughness values below 0.02 μm, enabling the characteristic wringing . This abrasive process iteratively corrects flatness by removing microscopic peaks, with grits selected for their hardness to handle materials like and without excessive wear. Quality control is integrated at multiple stages to ensure and reliability. In-process monitoring includes to measure central against standards and air gauging to assess surface flatness and parallelism non-destructively. Final inspections verify all parameters, with blocks rejected if they exceed allowable deviations; high-grade production typically achieves rejection rates under 1% through rigorous process controls. Modern advancements enhance efficiency and precision in gauge block fabrication. Computer numerical control (CNC) systems automate and grinding operations, allowing programmable paths for consistent pressure and motion to reduce operator variability. Laser etching applies identification markings, such as serial numbers, directly onto the block surface without compromising flatness.

Historical Development

Invention and Early History

Prior to the invention of gauge blocks, precision measurement in relied primarily on line standards, such as meter bars, which defined between engraved lines on a bar. These standards were inherently limited for applications, as they were susceptible to wear on the graduation lines, errors during reading, and environmental factors like variations that could alter the material's dimensions, making them impractical for direct, repeatable end-to-end gauging in production settings. The gauge block was invented by Swedish machinist Carl Edvard Johansson in 1896 while he served as an armorer-inspector at the rifle factory in , . Motivated by the need for interchangeable rifle parts during military production, Johansson sought to create a versatile system that minimized the hundreds of individual limit gauges traditionally required for . He developed the concept of stacking precisely finished blocks end-to-end to form any desired length, leveraging their flat, parallel surfaces that could "wring" together through molecular for stable combinations. The first set, produced in 1899, consisted of 102 steel blocks made from high-carbon Swedish steel, heat-treated for dimensional stability, enabling measurements from 1 mm to 100 mm in 0.001 mm increments. Johansson filed for a patent in 1898, which was established in 1908 after an appeal as Swedish Patent No. 17017, titled "Gauge Block Sets for Precision Measurement," formalizing the wringing set design. Early adoption was gradual but impactful; by 1906, 28 Swedish firms and three international companies used his blocks, demonstrating their utility in reducing gauging complexity. In 1918, the establishment of C.E. Johansson Incorporated marked a key milestone, facilitating the introduction of gauge blocks to American , including early collaboration with the for precision gauging in automotive manufacturing. This adoption highlighted the blocks' role in enabling on a large scale, though full integration by Ford occurred later in the 1920s.

Modern Evolution and Standards

In the 1920s, the National Bureau of Standards (NBS, now NIST) played a pivotal role in adopting gauge blocks for national , initiating collaborative projects with industry leaders like to establish standardized length measurements. A key milestone occurred in 1929 when NBS purchased a set of high-precision gauge blocks from inventor Carl Edvard Johansson to serve as reference standards, enabling uniform practices across manufacturing sectors. By the mid-20th century, advancements in materials led to the introduction of gauge blocks, which offered superior durability and stability compared to , particularly for master reference sets in controlled environments. These blocks, prized for their low and resistance to wear, became widely used in by the 1950s, extending the lifespan of standards in industrial applications. Standardization efforts intensified in the late to ensure global interoperability. The (ASME) published B89.1.9 in 1984 (with revisions in 1997), specifying design and metrological characteristics such as length deviations, flatness, and for rectangular and square cross-section gauge blocks. This was updated in 2002 and again in 2023 to better align with international practices, incorporating tolerances that facilitate cross-border trade while maintaining U.S. rigor. Complementing this, the (ISO) first published 3650 in 1978, with a second edition in 1998 defining similar parameters for gauge blocks up to 500 mm, including four accuracy grades based on maximum length deviations and parallelism limits, promoting harmonized worldwide. In the 2020s, has evolved toward digital integration, with digital twins—virtual replicas of physical gauge blocks—enabling simulated calibration and to reduce physical handling and enhance accuracy in Industry 4.0 environments. These models, calibrated against , support virtual verification of length standards without direct contact, addressing challenges in high-volume production. Concurrently, ceramic gauge blocks, particularly those made from zirconia, have gained dominance in high-tech sectors like and semiconductors due to their coefficient of approximately 9.5 × 10^{-6}/K, exceptional wear resistance, and corrosion immunity, ensuring long-term stability in demanding conditions. The 2019 redefinition of the (SI) by the International Bureau of Weights and Measures (BIPM) further solidified gauge blocks' role in metrological , linking them directly to fundamental constants like the for the . Post-redefinition, gauge block calibrations via provide unbroken chains to the SI, enhancing global consistency and reducing uncertainties in length dissemination for national metrology institutes.

Gauge Pins

Gauge pins, also known as pin gages, are precision cylindrical tools primarily used for go/no-go gauging of internal diameters in bores and holes. These hardened pins feature diameters typically ranging from 0.05 mm to 25 mm, allowing for quick assessment of whether a machined hole conforms to specified tolerances by attempting insertion—the "go" pin fits if the hole is within the lower limit, while the "no-go" pin does not if it exceeds the upper limit. They are essential in metrology for inspecting small to medium-sized features in manufacturing, such as drilled holes or slots, ensuring dimensional accuracy without the need for complex measuring equipment. Constructed from high-quality materials like 52100 chrome alloy steel hardened to 58-62 Rockwell C for durability and wear resistance, gauge pins often incorporate carbide for enhanced longevity in high-volume applications. The ends are typically ground with a slight chamfer or hemispherical radius to facilitate smooth insertion and prevent damage to delicate hole edges, while the cylindrical body maintains strict roundness and straightness. Tolerances for these pins are governed by ANSI/ASME B89.1.5, which specifies classes such as XX, X, Y, Z, and ZZ, with deviations as fine as ±0.00002 inches (0.0005 mm) for the highest precision grades, ensuring reliable performance as master standards. In usage, gauge pins are inserted directly into the workpiece bore to verify internal diameters, with sets providing comprehensive coverage across size ranges in increments as small as 0.001 mm for versatile application in . These sets, often housed in protective cases, enable efficient testing for hole size, location, depth, and even setting adjustable instruments like micrometers. Unlike gauge blocks, which rely on flat surfaces and wringing for linear measurements, gauge pins leverage to accurately assess circular features without alignment concerns, and they are calibrated using precision micrometers or supermicrometers traceable to national standards. This design prioritizes simplicity and speed for internal gauging tasks, sharing core precision principles with gauge blocks but adapted for cylindrical geometries.

Gauge Rollers and Balls

Gauge rollers are precision cylindrical tools, typically used in pairs, to measure the thickness of gear teeth or external radii in metrological applications. These rollers are placed in the spaces between adjacent gear teeth, allowing the distance over the rollers to be measured with a micrometer or , which provides data on tooth thickness according to standards like ANSI/AGMA 2002-B88. Diameters range from 5 mm to 50 mm, selected based on the gear module to ensure proper seating without interference, enabling accurate assessment of profiles in and helical gears. Gauge balls, in contrast, are spherical precision standards employed for measuring internal threads via the three-wire method or in ball micrometers for curved surfaces. Constructed from for enhanced wear resistance and dimensional stability, these balls have diameters from 1 mm to 25 mm, with size tolerances of ±0.00254 mm and roundness deviations limited to 0.5 μm to maintain measurement integrity. They facilitate pitch diameter verification in threads and contact-based inspections of concave features, often in setups. Both gauge rollers and balls find key applications in setting up optical comparators for profile projection and verifying fillet radii in machined components, where their high and cylindricity ensure point-contact accuracy without distortion. Tolerances around 0.5 μm for roundness align with the precision required for sub-micrometer verifications in , governed by standards such as ISO 3290 for balls. They are calibrated using methods traceable to national standards, complementing gauge block assemblies in hybrid setups for extended linear references.

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