Thread Gauges

What are thread gauges?

A thread gauge is used to check whether a threaded part fits within a certain tolerance or standard. An important distinction is that a thread gauge will only check or ‘gauge’ the thread and not measure the thread itself.

Thread plug and thread ring gauges contain both ‘Go’ and ‘No-Go’ threads. If a component or part is compatible with the ‘Go’ thread, this indicates that the component is within the given tolerance of the gauge. If the component screws onto a ‘No-Go’ thread, the component is to the incorrect tolerance and should be corrected or discarded.

What different types of thread gauge are there?

Thread gauges are predominantly available as either a plug gauge or ring gauge.

A plug gauge is used to measure internal (female) threads like those found on nuts or tapped holes. On most sizes, plug gauges are double ended, with the Go and No-Go threads found on the same gauge handle. The No-Go thread on plug gauges are larger than the Go thread to indicate the upper limit of the gauge tolerance. Most plug gauges conform to a 6H class or tolerance, however other classes like 6G and 4H are also available.

A ring gauge is used to measure external (male) threads like those found on screws or studs. Ring gauges usually come in pairs, with one ring being the Go thread and the other the No-Go thread. The No-Go thread on ring gauges are smaller than the Go thread to indicate the lower limit of the gauge tolerance. Most ring gauges conform to a 6g class or tolerance, however other classes like 6e and 6h are also available.

Tapered threads (NPT & BSPT) are checked using a stepped or tapered thread gauge. These gauges check the effective diameter of the tapered thread at a standard length from the component face. When mating components are fitted together, a seal is formed on the taper at a given position. The tapered gauge is screwed into or onto the component. The start of the thread or component face should stop between the upper and lower limit on the gauge (the flat section).

What thread forms are thread gauges available in?

Thread gauges are available for all possible thread forms. Included in Cutwel’s range are thread ring and thread plug gauges designed for measuring Metric Fine, Metric Coarse, BSP(G), BSPT, BSW Whitworth, BSF, NPT, NPTF, UNC, UNF, UN, UNEF, UNJC, Metric Fine Conduit, PG, Thread Repair (STI) & Trapezoidal threads.

What brands of thread gauges do we supply?

Cutwel supply thread gauges from Insize and premium German brand JBO. Insize thread gauges are perfect for general workshop gauging, whereas JBO thread gauges are ideal for inspection-grade environments with a wider range of sizes, tolerances and thread forms available.

Can you calibrate thread gauges?

All thread gauges can be calibrated. Standard thread gauge calibration includes the measuring of the major diameter, minor diameter, pitch diameter and the thread angle.

Our Insize gauges can be requested to be calibrated to a UKAS standard, which is the United Kingdom Accreditation Standard by which all gauges are assessed. JBO gauges can be supplied with a German standard of accreditation (DKD certification). In most general workshop environments, calibration shouldn’t be required as each gauge is supplied with a manufacturer’s inspection certificate as standard.

Different levels of calibration and UKAS calibration is available. Contact Cutwel today for more information on the levels of calibration we can offer.