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Gauge block

Metric gauge block set

A gauge block (also known as a gage block, Johansson gauge, slip gauge, or Jo block) is a precision ground and lapped length measuring standard. It is used as a reference for the setting of measuring equipment used in machine shops, such as micrometers, sine bars, and dial indicators (when used in an inspection role).



36 original Johansson gauge blocks wrung together, held together solely by the adhesion of their extremely flat surfaces. 1907.

Shown at top is an image of a metric gauge block set. The set consists of a range of varying size blocks, along with two wear blocks.

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, with the minimum number of blocks. The wear pieces are included at each end of the stack whenever possible as they provide protection against damage to the lapped faces of the main pieces. After use the blocks are reoiled or greased to protect their faces from corrosion.


Wringing is the process of sliding two blocks together so that their faces lightly bond. When combined with a very light film of oil, this action excludes any air from the gap between the two blocks. The alignment of the ultra-smooth surfaces in this manner permits molecular attraction to occur between the blocks, and forms a very strong bond between the blocks along with no discernible alteration to the stack's overall dimensions. Gauge blocks, when properly wrung, may withstand a 200 lb (890 newton) pull. The detailed physics responsible for this phenomenon remains unclear.[1] Possible causes that have been suggested are: atmospheric pressure, molecular attraction, a minute film of oil, or a combination of these factors.

Accessory set

Gauge block accessory set

The pictured accessories provides 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 and scribers.

Slip gauges are made from a select grade of carbide with hardness of 1500 Vickers hardness. Long series slip gauges are made from high quality steel having cross section (35 x 9 mm) with holes for clamping two slips together.


They are available in various grades depending on their intended use.[2]

  • reference (AAA): small tolerance (± 0.00005 mm or 0.000002 in) used to establish standards
  • calibration (AA): (tolerance +0.00010 mm to -0.00005 mm) used to calibrate inspection blocks and very high precision gauging
  • inspection (A): (tolerance +0.00015 mm to -0.00005 mm) used as toolroom standards for setting other gauging tools
  • workshop (B): large tolerance (tolerance +0.00025 mm to -0.00015 mm) used as shop standards for precision measurement

More recent grade designations include (U.S. 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 U.S. 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.


The gauge block set, also known as "Jo Blocks", was developed by the Swedish inventor Carl Edvard Johansson.[3] Johansson was employed in 1888 as an armourer inspector by the state arsenal Carl Gustaf Stad's Rifle Factory in the town of Eskilstuna, Sweden. He was concerned with the expensive tools for measuring parts for the Remington rifles, then in production. When Sweden adopted the Mauser carbine in 1894 Johansson was very excited over the chance to study Mauser's methods of measuring. However, a visit to the Mauser factory in Oberndorf turned out to be a disappointment. On the train home he started thinking about the problem and came up with the idea of a set of blocks that could be combined to make up any measure.

Back home Johansson converted his wife's sewing machine (a Singer 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 a lot with the grinding beside the household works. 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 Martin Leland at Cadillac Automobile Co. around 1908. The first manufacturing plant in America for his gauge block sets was established in Poughkeepsie, Dutchess County, New York in 1919. The economy did not turn out so well for the company so in 1923 he wrote a letter to Henry Ford, at 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. He stayed for 12 years at Ford. At the age of 72, in 1936, he 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, posthumously in 1943, shortly after his death.

Gauge pins

Similar to gauge blocks, these are precision ground cylindrical bars for use in Go-NoGo gauges or similar applications.

Gauge rollers and balls

These are supplied as sets of individual rollers or balls as used in roller or ball bearings



  • Althin, Torsten K.W. (1948), C.E. Johansson, 1864–1943: The Master of Measurement, Stockholm: Ab. C.E. Johansson [C.E. Johansson corporation], LCCN 74-219452 .
  • Krar, Steve F.; Gill, Arthur R.; Smid, Peter (2005), Technology of Machine Tools (6th ed.), McGraw-Hill Career Education, ISBN 978-0-07-723225-2 .

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