Gauge Block - Grades

Grades

Gauge blocks are available in various grades, depending on their intended use. 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) used to establish standards
• calibration (AA): (tolerance +0.10 μm to −0.05 μm) used to calibrate inspection blocks and very high precision gauging
• inspection (A): (tolerance +0.15 μm to −0.05 μm) used as toolroom standards for setting other gauging tools
• workshop (B): large tolerance (tolerance +0.25 μm to −0.15 μm) 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. Also consult page 2 of: Commercial Gauge Block Tolerances (Length refers to the calibrated thickness)