The NO GO plug gauges for British BSW threads are inspection tools designed to verify the upper acceptance limit of internal British Standard Whitworth threads according to BS 84. They are used to check that the threaded hole is not oversized, excessively worn, deformed or out of tolerance, ensuring correct functional engagement with the corresponding male component. They are suitable for mechanical parts, industrial spare parts, British-standard machinery, equipment, vintage vehicles, inch-based fastening systems and technical components with Whitworth threads.

Unlike GO gauges, these plug gauges perform the NO GO function only: they must not screw into the internal thread beyond the specified limit. If the NO GO gauge enters too far, the thread may be out of tolerance, too large, worn or unsuitable for the required mating function. This type of inspection is essential when it is not enough to verify that the thread accepts engagement, but it is also necessary to exclude excessive clearance, loss of accuracy, unstable assembly or threads that are not suitable for final mounting.

British Standard Whitworth threads use a 55° profile and are still found in many industrial applications, especially on older machinery, British-origin components, spare parts, equipment, vintage vehicles and mechanical systems with inch-based threads. It is important to correctly distinguish BSW gauges from UNC, UNF, BSP, NPT or metric gauges, because profile, pitch, thread angle and mating compatibility are not interchangeable. Using an incorrect plug gauge may lead to wrong inspection results, thread damage or acceptance of non-conforming parts.

For reliable checking, the NO GO plug gauge must be used on clean threads, free from chips, burrs, oxides, dirt or machining residues. During inspection, correct coaxial alignment with the threaded hole must be maintained and the gauge must never be forced, because the NO GO plug gauge is used to indicate the tolerance limit and must not be used as a thread repair or correction tool. Misaligned or forced use may damage both the gauge and the inspected component. These plug gauges are suitable for mechanical workshops, quality control, maintenance technicians, toolrooms, technical restoration, vintage automotive work, mechanical engineering and industrial repair operations where internal British BSW threads must be checked quickly and repeatably.

ACCREDIA certification or a calibration report can be supplied on request; because the item must be sent to the inspection or certification body, this documentation may increase delivery time.