How to Determine and Select the Proper Tolerance

How to Determine and Select the Proper Tolerance for Your Gauging Application

The normal rule of practice requires 10 % of product tolerance to divided between the ‘GO and NOGO”gauges. For plug gauges, a plus tolerance is applied to the GO member and a minus tolerance to NOGO member. Ring gauges receive reverse tolerance direction so that the GO member is a minus an the NOGO is plus tolerance. Applying this result practice results in gauge tolerance always being included in the part tolerance by up to 10%. This results in the possibility that 10% of good product could fail inspection that no bad product would ever pass.

 

GAGEMAKER’S TOLERANCE CHART

(PLAIN PLUG & RING GAUGES)

ABOVE
TO & INCLUDE
CLASS XX
CLASS X
CLASS Y
CLASS Z
0.010″
.254mm
0.825″
20.95mm
0.000020″
0.5µm
0.000040″
1.0µm
0.000070″
1.75µm
0.0001″
2.5µm
0.825″
20.95mm
1.510″
38.35mm
0.000030″
0.75µm
0.000060″
1.5µm
0.000090″
2.25µm
0.00012″
3.0µm
1.510″
38.35mm
2.510″
63.7mm
0.000040″
1.0µm
0.000080″
2.0µm
0.00012″
3.0µm
0.00016″
4.0µm
2.510″
63.75mm
4.510″
114.55mm
0.000050″
1.25µm
0.0001″
2.5µm
0.00015″
3.75µm
0.00020″
5.0µm
4.510″
114.5mm
6.510″
165.35mm
0.00065″
1.625µm
0.00013″
3.25µm
0.00019″
4.75µm
0.00025″
6.25µm
6.510″
16.35mm
9.010″
228.85mm
0.000080″
2.0µm
0.00016″
4.0µm
0.00024″
6.0µm
0.00032″
8.0µm

* Table 1, pg. 4 of ANSI B89.1.6 2002 specifications

Proper Care Usage of Gauges

  • Parts Dimensions to be gauged should be free of burrs to prevent gauging interference.
  • Gauges should be turned or pushed slowly and gently. Forcing gauges will result in faulty gauging and possibility of damaging both the gauge and the part.

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