What is a thread plug gauge? A thread plug gauge is a fixed limit gauge that checks internal threads, such as tapped holes and nuts. Its GO end must screw in fully and its NO-GO end must not enter beyond the allowed turns. It confirms a thread is within tolerance without measuring individual dimensions.
What is a thread ring gauge? A thread ring gauge is a fixed limit gauge that checks external threads, such as bolts, studs and screws. The GO ring must run along the full thread, and the NO-GO ring must not pass beyond the allowed turns. GO and NO-GO rings are usually supplied as a pair.
A thread gauge checks whether a thread meets its specified size and form. A thread plug gauge inspects internal threads, and a thread ring gauge inspects external threads. GO and NO-GO members confirm the thread is within tolerance using a simple pass or fail check.
Thread gauges give a fast, reliable accept or reject decision. They check thread fit without measuring every dimension. A plug gauge screws into an internal thread; a ring gauge fits over an external thread.
A thread plug gauge checks internal threads, while a thread ring gauge checks external threads. GO/NO-GO thread gauges confirm thread acceptance without measuring each thread element separately.
| Gauge | Inspects | GO result | NO-GO result |
|---|---|---|---|
| Thread plug gauge | Internal threads | Should screw in fully | Should not enter beyond allowance |
| Thread ring gauge | External threads | Should screw on fully | Should not pass beyond allowance |
| Feature | Thread plug gauge | Thread ring gauge |
|---|---|---|
| Thread checked | Internal (tapped holes, nuts) | External (bolts, studs, screws) |
| Form | Threaded plug, often double-ended | Threaded ring, GO and NO-GO as separate rings |
| GO check | Must enter full thread length | Must run full thread length |
| NO-GO check | Must not enter beyond allowed turns | Must not pass beyond allowed turns |
| Typical use | Machining, tapping, incoming inspection | Fastener production, turned parts |
The GO member should engage fully with a conforming thread. The NO-GO member should not engage beyond a small specified allowance. Together they confirm the thread is within tolerance without measuring individual dimensions.
The GO member of a thread gauge must assemble fully with the part by hand. The NO-GO member of a thread gauge must not engage beyond the permitted number of turns. Thread gauges should never be forced, because force can damage both the gauge and the part.
Thread gauges are available for metric, BSP, BSW, NPT and other common thread forms. Confirm the exact forms and sizes stocked from the live product listing below.
Select by thread form, nominal size and tolerance class. Match the gauge to the drawing callout. Use plug gauges for internal threads and ring gauges for external threads. Contact BTSA to confirm availability for your specific thread form.
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Ordering a thread gauge requires the thread standard, nominal size, pitch and tolerance class.
It checks whether a thread meets its specified size and form using GO and NO-GO members.
A plug gauge checks internal threads. A ring gauge checks external threads.
The GO member should engage fully. The NO-GO member should not, confirming the thread is in tolerance.
Common forms include metric, BSP, BSW and NPT. Confirm availability from the live product listing.
Yes. They are calibrated against traceable standards. Contact BTSA for calibration support.
The thread standard, nominal size, pitch, tolerance class and whether you need a plug, ring or both.
It depends on usage volume and your quality system. High-volume GO gauges wear faster and need shorter intervals.
Yes. A worn GO gauge can accept threads that are out of tolerance.
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Thread gauges wear with use, especially the GO member. Wear can let out-of-tolerance threads pass. Periodic calibration checks pitch diameter and other thread elements against traceable standards.
Worn GO thread gauges can accept out-of-tolerance threads, so periodic calibration is essential.
