10% Product Tolerance Rule ASME B89.1.5:1998 p 4.1

The 10% product tolerance rule is commonly used in the manufacturing industry. It is considered a "rule-of-thumb" which means that it is a suggestion or a starting point. You, as the engineer, may use the 10% product tolerance rule, or deviate from the 10% product tolerance rule, as long as you can justify your decision to your management.

To calculate the gage tolerance using the 10% product tolerance rule:
1. Calculate the full tolerance of the product feature.
2. Calculate 10% of the product feature tolerance to find the full gage tolerance.
3. Divide the full gage tolerance in half to find the gage member tolerance.
(Otherwise stated: Product Tolerance x 0.05 = Gage Member Tolerance)

Standards that relate to gage design decisions:
ASME B89.7.3.1 Guidelines for Decision Rules: Considering Measurement Uncertainty Determining Conformance to Specifications
ASME B89.1.5 Measurement of Plain External Diameters for use as Master Discs or Cylindrical Plug Gages
ASME B89.1.6 Measurement of Plain Internal Diameters for use as a Master Rings or Ring Gages
These standards are available for purchase from ASME

General Statements:
The tightest tolerance for plain cylindrical gages which is feasible to be used to test parts is X. Tolerances XX and XXX plain cylindrical gages should not be used to test parts. Tolerances XX and XXX are better suited for master gages; not working gages. When the part tolerance becomes tight enough to warrant the use of XX or XXX plain cylindrical working gages; then Air Gages need to be considered as the better alternative.

When tolerance XX or XXX are supplied; we do not argue with the manufacturer’s certification. It is difficult to get two calibration laboratories to return identical calibration results for tolerances XXX plain cylindrical gages. With tolerance XX we should be able to gain agreement between different calibration laboratories; however; the test method needs to be identical and the uncertainty needs to be ignored.