This product is a 7/8" BSW HSS dienut, a circular cutting die designed to restore, clean or cut external British Standard Whitworth (BSW) threads on bolts, studs and rods. It is intended for use in a standard die stock or holder to cut or reform 7/8" BSW threads where imperial Whitworth fastenings are required, such as repair work, restoration or on-site maintenance.

The dienut is manufactured from high speed steel (HSS, nominally M2 grade) and is heat treated and ground to give a durable cutting edge with good red hardness and wear resistance. The thread form is BSW (British Standard Whitworth), with the characteristic 55° thread angle and rounded crests and roots, providing compatibility with traditional Whitworth fasteners. The die is supplied with an oil protective finish to reduce surface corrosion during storage and use, and the HSS material allows occasional regrinding for extended service life.

Typical applications include engineering maintenance, classic vehicle and motorcycle restoration, railway and steam heritage work, agricultural machinery servicing and general industrial repair where Whitworth-threaded components remain in service. The dienut is especially useful for machinists and fitters who need a portable method of re-forming damaged external threads or cutting new threads onto existing shafts where BSW is the required standard.

Key benefits of this HSS dienut are its wear resistance at elevated cutting temperatures, toughness to resist chipping, and suitability for use on mild steel, low alloy steels and most common engineering materials. Because it uses the Whitworth profile it is compatible with existing BSW bolts and nuts; being an HSS tool it offers a longer life than carbon steel dies and can be sharpened if necessary. It is compatible with standard handheld die stocks and machine die holders designed for round dies.

Duchy Fasteners stocks a comprehensive range of imperial hand and machine dies and dienuts, including Whitworth sizes. The 7/8" BSW dienut is available individually, and we also supply matching BSW tap and die sets and replacement packs across the imperial range to suit workshop and on-site requirements.