This product is a 1-inch BSW (2-inch long) right-hand split die designed for cutting, repairing and truing external Whitworth threads on shafts and studs. The split die format allows clamping adjustment to open or close the cutting face slightly, making it ideal for restoring worn threads, achieving a controlled fit or cutting threads to exact tolerances by hand or in a machine die holder.

The die is manufactured from high speed steel (HSS), typically M2 grade, providing a good balance of toughness and hot hardness for cutting carbon steels, alloy steels, non-ferrous metals and castings. The cutting faces are ground to the Whitworth form in accordance with the Whitworth thread profile as specified by BS 84, producing the characteristic 55° thread flank with the appropriate root and crest radii for BSW fittings. The unit is finished with a precision ground seating face and a protective black oxide (or passivated) surface to reduce flash rust and aid chip evacuation. This is a right-hand (RH) thread tool intended for conventional clockwise threading.

Typical applications include maintenance and restoration of classic British machinery and vehicles, agricultural and marine repair, heritage engineering, instrument and pump rebuilding, and general workshop use where imperial Whitworth threads remain in service. Trades most likely to use this die are mechanical engineers, motor vehicle restorers, HVAC and plumbing engineers working on older pipe fittings, and maintenance technicians in facilities with legacy equipment.

Key benefits of the HSS split die are improved wear resistance compared with carbon tool steels, the ability to withstand the heat generated during cutting, and the adjustable split which lets the user tighten or loosen the die to achieve the desired thread fit or to compensate for die wear. It is compatible with standard die stocks and machine die holders for both hand and powered threading operations. When used correctly with suitable cutting lubricant it produces clean, accurate BSW threads that mate with BS-standard nuts and bolts.

Duchy Fasteners stocks a broad range of HSS split dies and matching die nuts in both imperial and metric series, available individually and in multi-size packs to suit workshop and professional requirements. Sizes and pack options are available on request.