Gauge blocks

Gauge blocks, (also known as gage blocks, Johansson gauges, or slip gauges) are precision ground and lapped measuring standards. They are used as references for the setting of measuring equipment such as micrometers, sine bars, dial indicators (when used in an inspection role).

Related Topics:
Micrometer - Sine bar - Dial indicators - Inspection role

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They are available in various grades depending on their intended use.http://claymore.engineer.gvsu.edu/~jackh/eod/manufact/manufact-116.html#pgfId-141526.

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• reference (AAA) — high tolerance (± 0.00005mm or 0.000002")
• calibration (AA) — (tolerance +0.00010mm to -0.00005mm)
• inspection (A) — (tolerance +0.00015mm to -0.0005mm)
• workshop (B) — low tolerance (tolerance +0.00025mm to -0.00015mm)

More recent grade designations include (U.S. Federal Specification GGG-G-15C):

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• 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:

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• 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.

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