TOLERANCE OF GAGES

IMPORTANT NEWS!

The difference between a Class Z gage and Class ZZ gage is the deviation allowed in the manufacturing process of the gage. Helpful reference materials are as follows:

ANSI Standard B89.1.5-1998 STANDARD
Description: This Standard is intended to establish uniform practices for the measurement of master discs or cylindrical plug gages to a given tolerance using vertical or horizontal comparators and laser instruments. The Standard includes requirements for geometric qualities of master discs or cylindrical plugs, the important characteristics of the comparison equipment, environmental conditions, and the means to assure that measurements are made with an acceptable level of accuracy. This Standard does not address thread or gear measuring wires.

The class or grade of a gage is determined during the manufacturing process.

ANSI Standard B89.7.3.1-2001
Description: These guidelines provide terminology and specify the content that must be addressed when stating a decision rule used for deciding the acceptance or rejection of a product according to specification.

Determining lifespan, wear, or calibration frequency of a gage is a combination of many factors such as material, actual deviation, surface finish, and uses in contact or non contact applications.

Plug Gage Tolerances
Description: Standard practice is to allow 5% of the hole tolerance for the GO gage and 5% for the NOGO gage tolerance. The Go gage whose nominal size is at the low limit of the hole to be checked is usually given a plus tolerance in order to insure all parts are within the low limit. The NOGO gage pin nominal size is at the high limit and is given a minus tolerance. There are several reasons for using finer tolerance gages than the 10% rule. In a production process where a large number of parts are expected to fall within the 5% areas of product tolerance ( near the high or low limits) which may result in parts being rejected due to gage tolerance, a tighter tolerance gage should be considered, therefore reducing the likelihood of rejecting an acceptable part. Cost of the gage versus the value of the parts play a vital element in this decision.

To read more information about our plug gages and other products we offer, visit our page on the ABC's of Plug Gages.