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Introduction
Introduction The American National Standards Institute defines a gage as "a device
for determining whether or not one or more dimensions of a manufactured part are
within specified limits." A plug gage is a cylinder designed to check the component
tolerance of a hole in a product. The plug gage has been found to be highly accurate,
economical and convenient for small hole inspection where a determination is made
of compliance with designed limits.
GO and NOGO gaging with plug gages provides a complete check of the dimensions of
a hole. If GO-NOGO gaging is used, there is no need to measure the size of a hole
to be certain that it is within the design limits. The proper use of plug gages
therefore eliminates the need for complex and expensive measuring equipment.
If a GO gage is used to verify the lower limit and a NOGO gage to verify the upper
limit of a hole, inspection is precise, clean cut and extremely simple. Inspection
with plug gages requires no training or experience in the interpretation of numerical
readouts or results which are necessary if measuring instruments are used. By using
plug gages an "inspector" has only to determine whether a gage is entering or not
entering a hole.
With plug gages, accuracies are possible in the order of .0000005" under proper
conditions of hole and gage quality, cleanliness, and temperature control, similar
to conditions normally required for any precise inspection.
In addition to eliminating any complicated measuring instruments, no set-up time
is required in using plug gages; thus a plug gage can be brought into use more quickly
and economically with no loss of accuracy.
Finally a plug gage, having a fixed dimension, requires no set-up, cannot get out
of calibration nor is it affected by cumulative error.
Plug gages should be used in a GO-NOGO combination. The purpose of the GO gage is
to determine whether the hole has met the low limit of the specifications. If a
hole is to small the GO gage will not enter. The larger NOGO gage checks the upper
limit of the hole. If the hole is too large the NOGO gage will enter. When the GO
gage enters and the NOGO gage is unable to enter the design specifications of the
hole have been met.
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