Thread Gauges

Thread gauges are the go/no-go check that confirms whether a threaded feature — a tapped hole or a turned external thread — is within tolerance before it goes to assembly. The go gauge enters cleanly; the no-go gauge stops at the first turn. If both conditions are met, the thread passes. No measuring, no calculation, no ambiguity.

We stock a large range covering metric and imperial threads, including plug gauges for internal threads (6H tolerance) and ring gauges for external threads (6g tolerance). Common sizes run from M4 × 0.7 through M8 × 1.25 and well beyond, with right-hand and left-hand forms across the range. All gauges are manufactured to BS/ISO standards for use in production inspection, incoming QC, and machine setup.

With thousands of gauges held in UK stock, you can spec a single gauge for a repair job or kit out an inspection station for a full production run. Orders before 4pm ship same day.

Plug gauges vs. ring gauges — which do you need?

Use a plug gauge to check a tapped hole — it tests the internal thread. Use a ring gauge to check a stud, bolt or turned diameter — it tests the external thread. For a complete go/no-go check on a thread pair, you need both. If you're unsure which gauge matches your specification, each product page lists the thread form, tolerance class, and pitch for that gauge.