This is a 1/2"-12 BSW HSS dienut, a hand tool used to cut, restore or chase external imperial threads on studs, bolts and round bar to the British Standard Whitworth (BSW) form. It is primarily intended for workshop use where 1/2" diameter, 12 threads per inch Whitworth threads are required, for repair or production of external threads on mild steel, alloy steels and other machinable materials.

The die is manufactured from high speed steel (HSS), typically M2 grade, and is hardened and tempered to retain cutting edges at elevated temperatures. The cutting face is ground to the BSW thread profile with a 55° Whitworth thread angle and rounded crests/roots in accordance with the British Standard Whitworth thread form. The tool is supplied with a bright/ground finish and a light protective oil to resist corrosion during storage. The dienut is presented in a hexagonal body so it can be operated with a standard spanner or fitted into a suitable die holder designed for round dies.

Typical applications include maintenance and restoration of classic British motor vehicles and motorcycles, marine and agricultural repairs, general engineering workshops and any installation where original Whitworth fasteners are used. It is particularly valuable in heritage restoration, plant maintenance and on-site repair where re-cutting damaged external threads avoids the need for replacement fasteners or components.

Key benefits of this HSS dienut include superior wear resistance and edge retention compared with carbon steel dies, good heat resistance for sustained cutting, and accurate thread form that ensures compatibility with existing BSW bolts and nuts. The hardened M2 HSS material offers a long service life when used with appropriate cutting lubricant; the hex body ensures positive drive with common hand tools and die stocks.

Duchy Fasteners holds a comprehensive range of taps, dies and dienuts in imperial and metric sizes. This 1/2"-12 BSW HSS dienut is available as a single item and as part of boxed die sets; please contact us for stock sizes and pack options.