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Threaded Master Set Plug Tolerances

Threaded Master Set Plug Tolerances.

It is assumed that if you are reading this you are involved in manufacturing. Being in manufacturing you know that all the parts you make have a tolerances applied to the nominal product dimensions. Threaded Master Setting Plug Gauges are no different.

Threaded Master Setting Plug Gages are defined by ANSI B1.2-1983; Gages and Gaging for Unified Inch Screw Threads which was Reaffirmed 2001. I expect that similar definitions exist in other standards, but this discussion does not directly address other standards.

W-tolerance is the specified tolerance for thread master setting plug gauges per ANSI B1.2; Page 143; Paragraph 5.13; W Tolerance Thread-Setting Plug Gages. The parameters which define W-tolerance are specified on ANSI B1.2; page 25; Table 7. The general rule-of-thumb is that W-tolerance as half of X-tolerance.

The advantages of the W-tolerance is:
1. The working gauge set with a W-tolerance thread master setting plug gage will be set closer to the maximum product tolerance limits which will allow more products to be viewed as good when presented to the working gauges.
2. Working gages set with W-tolerance thread master setting plug gauges will have less disagreements between themselves.
The disadvantages of the W-tolerance is:
1. W-tolerance thread master setting plug gages may require replacement more often than X-tolerance thread master setting plug gauges.
2. W-tolerance thread master setting plug gages are usually priced at a premium.

X-tolerance is allowed by an interpretation of ANSI B1.2; Page 17; Table 5; Note (2): "Tolerances greater than W tolerance for pitch diameter are acceptable when internal indicating or snap gage can accommodate a greater tolerance and when agreed upon by supplier and user." Based on this note, gauge makers offer X-tolerance thread master setting plug gages as the industry standard. If you want W-tolerance you must specify W-tolerance when requesting the price quotation. When X-tolerance is offered on setting plug gauges it is translated as meaning: X-tolerance on Pitch Diameter; W-tolerance on Lead; W-tolerance on Half-Angle; W-tolerance on Minor Diameter.

When ordering a X-tolerance thread master setting plug gage, you may receive a thread master setting plug gauge which is certifiable to both X-tolerance and W-tolerance. The reason is that the entire W-tolerance is contained within the greater X-tolerance.

For standard sized thread master setting plug gages the gauge maker may manufacture multiple copies at one time. If you desire a standard size W-tolerance thread master setting plug gage, the gauge maker just needs to search through his inventory to find one of the in-stock X-tolerances thread master setting plug gages which also meets the requirements of the W-tolerance. The gauge maker will usually charge more for the W-tolerance threaded master setting plug gage. The extra charge is assessed because the tolerance is tighter and it takes more effort to make the W-tolerance thread master setting plug gauge, or on standard sizes, more effort to do an internal sort.

Other related pages:
Set Plug Usage.
Adjusting Thread Ring Gage Locking Device.
Procedures for Setting Thread Ring Gages with Truncated Setting Plug Gages

This data current as of May 2008
Refer comments/corrections to gageguy@gagecrib.com.

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