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Metrology

Thread Quality Control Series: Go and No-Go Checks

Stop spinning gauges

Published: Monday, April 11, 2022 - 12:03

‘I just want to avoid spinning gauges all day.”

We hear this from manufacturing professionals all over the world. We were discussing this recently with a manufacturer in Wisconsin that machines large quantities of threaded parts. Their customer requires them to “go” and “no-go”-verify every part. They were dealing with this requirement the way many plants do: Operators stood by and spun a gauge into every thread with their fingers. Unfortunately, this method was not only burdensome but also allowed plenty of room for operator error and repetitive-motion injury.

Our mission at New Vista is to work with manufacturers like these to provide the knowledge and tools they need to overcome thread quality obstacles, so they can stop spinning gauges with their fingers. This article, as part of that mission, presents an introduction to thread gauging.

Attribute gauging vs. direct measurement

When it comes to production inspection of threads, there are two types of inspection to consider: attribute gauging and direct measurement. Attribute gauging ensures that a feature dimensionally falls within accepted pass/fail range, by means of a gauge. Direct measuring actually measures the feature to determine where it is within the acceptable range. For most threaded-parts manufacturing, attribute gauging is the more practical verification method due to its speed, simplicity, and low cost (especially in the case of internal threads).

Contact vs. noncontact gauging

Gauging threads is a contact inspection procedure. Although noncontact methods of inspecting threads exist, the traditional “go” inspection method with a physical gauge is preferable to guarantee that the thread will assemble properly with the mating part. Thread gauges for straight threads (the common metric and unified standard) are usually supplied as a “go” and “no-go” gauge set with a handle as shown here:


Go and no-go set

Pipe threads and other specialty threads entail unique gauging procedures that we will cover later. The most common types of thread checks for straight thread are “go” verification for pitch diameter and verification of the minimum thread length. For the vast majority of manufacturers, employing these two verifications at 100 percent is sufficient. When “no-go” gauging is employed, it’s typically only sampled, not checked 100 percent of the time.

‘Go’ checks

“Go” gauging, by its nature, is a composite check; it verifies several attributes all at once, and through that composite verification, it guarantees proper assembly. So, a “go” gauge for an internal thread would guarantee that the thread’s pitch diameter, the minor diameter, and the major diameter are all sufficiently large. If the gauge is employed advantageously, it will also guarantee that the thread is of sufficient length (i.e., depth).

‘No-go’ checks

“No-go” gauging, except in rare instances, can check only one attribute at a time. Manufacturers may be required to “no-go”-verify a thread’s pitch diameter or minor diameter. In either case, the “no-go” gauge ensures that the pitch or minor diameter isn’t oversized, which would cause the mating part to be loose. Standards differ depending on part material, thread size, and thread length, but the general rule of thumb is that the “no-go” pitch diameter gauge should not go more than two or three turns into the thread. Be sure to review your thread’s particular specifications. A “no-go” minor diameter gauge is as simple as using a gauge pin or gauge ball to ensure that it doesn’t enter the thread.

In situations where both “go” and “no-go” verification is required, New Vista has developed combination gauges that will perform both checks in one pass on through threads, saving time and costs.

Summary

The “go” and the “no-go” checks are a critical aspect of any manufacturing process involving threads. But you don’t have to do them with your fingers. If you would like to find out how you can expedite your thread inspection process, or if you have additional questions about thread gauging, contact one of New Vista’s Applications engineers today. Expert applications service is available from our U.S. location and in several other countries as well.

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About The Author

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New Vista

New Vista engineers have more than a century of cumulative engineering and automation experience. First organized within The J.L. Wickham Co. (founded in 1983), these engineers—and many others—designed and developed large machine systems for companies such as General Motors, Chrysler, John Deere, and Carrier Corp. Striking out on his own in 1992, Wickham Co. founder Jack Wickham formed New Vista Corp. to create a company focused on smaller (under $1 million) projects. With 18 years experience at Black & Decker Corp.—culminating in heading the manufacturing development group in the late 1970s—Wickham is uniquely experienced in tackling difficult production hurdles.