Go and No-G0 Gage Design Calculator

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Plug (Pin) and ring gauge design calculators

One of the most frequent questions asked is, “how do I choose a plug (pin) gauge for my measurement application.” Therefore I put together this webpage and calculator to help you understand and calculate the concept of fixed limit gauging.

Keep in mind the fundamental concept of fixed limit gauging is to never accept a bad part. In order to accomplish this the tolerance of the plug or ring will be designed to actually have the potential to reject good parts. When this method rejects good parts that are near the extreme limits of the part tolerance the part can be rechecked with a more accurate method to determine if the part is actually in tolerance.

In the following equations I don't want to get hung up about semantics. Some people call pin gauges, plug gauges, and others call plug gauges, pin gauges. Either way is acceptable.

Keep in mind that a hole Go plug has a plus tolerance and is designed to gauge the smallest acceptable hole size, and a hole No-Go plug has a negative tolerance, designed to gauge the largest acceptable hole size. Subsequently the Go gauge should be able to pass through the hole and a No-Go plug gauge should not. This is why they call it Go No-Go gauging. Others call it Fixed Limit Gauging.

The opposite is true for ring gauges on external diameters. A Go ring has a negative tolerance and is designed to gauge the largest acceptable external diameter and a No-Go ring has a positive tolerance and is designed to gauge the smallest acceptable external diameter.

Therefore:

Hole Pin Gauges Equations

Go Plug Minimum
Eq. 1
GP_Dia-max = MMC + Tolerance of gauge

Go Plug Maximum
Eq. 1a
GP_Dia-min = MMC

No-Go Plug Minimum
Eq. 2
NGP_Dia-min = LMC - Tolerance of gauge

No-Go Plug Max.
Eq. 2a
NGP_Dia-max = LMC

Ring guages for external diameters Equations

Go Ring Gauge Minimum
Eq. 3
GR_Dia-min = MMC - Tolerance of gauge

Go Ring Gauge Maximum
Eq. 3a
GR_Dia-max = MMC

No-Go Ring Gauge Maximum
Eq. 4
NGR_Dia-max = LMC + Tolerance of guage

No-Go Ring Gauge Minimum
Eq. 4a
NGR_Dia-min = LMC

MMC = Maximum Material Condition size
LMC = Least Material Condition size

It is easy to get confused between how the tolerance of the ring and plug is applied in relationship to the Go and No-Go member. Sometimes it is easier to think of the feature you are measuring in terms of more or less material. The reason is that a Plus tolerance applied to a plug makes the actual plug size larger. The plus Tolerance applied to a ring makes the ring gauge diameter small. Please keep this in mind when you follow the examples.

Gauge accuracy 10:1,5:1, 4:1 and 2:1 ratios of accuracy are avaialable within the calculator

Gauge sizing using the 10:1 (Imperial units) and the 4:1 (SI units) is the high range of guage accuracy as used industry and specified under Gauge American National Standard ANSI/NCSL Z540-1-1994 Clause 10.2.b. 10:1 or better is considered optimal in metrology, where 4:1 is considered the minimum in metrology.

Source:

ANSI/ASME STD B89.7.3.1-2001 "GUIDELINES FOR DECISION RULES: CONSIDERING MEASUREMENT UNCERTAINTY IN DETERMINING CONFORMANCE TO SPECIFICATIONS".
ANSI ASME B89.1.5

Kelly Bramble, ASME Certified Senior GDTP, FAA Airframe and Powerplant
Engineers Edge, LLC