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System for producing precision lengths by stacking components

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. 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. 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 The gauge's nominal length is also known as the interferometric length. 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). As detailed in the Grades section, each block has a size tolerance of a few millionths of an inch, so stacking them together introduces a cumulative uncertainty. 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).

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.

The gauge block set, also known as "Jo Blocks", was developed by the Swedish inventor Carl Edvard Johansson. 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. 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." In the early 20th century, the U. S. inch was effectively defined as 25.4000508 mm (with a reference temperature of ) and the U. K. inch at 25.399977 mm (with a reference temperature of ). with other manufacturers of gauge blocks following Johansson's definition by producing blocks designed to be equivalent to his. 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, effectively endorsing Johansson's pragmatic choice of conversion ratio. 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.

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.

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.