This is a 5/16" BSW (British Standard Whitworth) right‑hand split die, designed to cut or restore external Whitworth threads on imperial shafts and studs. The die is primarily used with a standard 1" die blank/profile and held in a compatible die stock for manual threading, or in a supported die holder for light machine work where appropriate.

The tool is manufactured from M2 high speed steel (HSS), hardened and ground to retain cutting edges and resist wear during repeated use. The split design allows fine adjustment of the effective thread size by tightening or loosening the split, and it gives improved chip clearance compared with solid dies. The product is supplied in a bright ground finish; selected items are available with black oxide for improved resistance to surface corrosion and reduced glare. The thread form is BSW (Whitworth), with the characteristic 55° thread angle and rounded root and crest, and this version is right‑hand (RH). Thread standards conform to the Whitworth form used for imperial fastenings, making it compatible with BSW nuts and threaded components commonly specified in British/heritage equipment.

Typical applications include maintenance and restoration of classic British vehicles and motorcycles, repair of agricultural and vintage machinery, marine refurbishment where Whitworth fittings remain in service, and general engineering workshops dealing with imperial fastenings. The die is suitable for cutting new threads on shafts, rechasing damaged threads and sizing studs back to Whitworth specification. When used with correct lubrication and appropriate die stock, the HSS construction provides good tool life and consistent thread profile.

Key benefits of this 5/16" BSW HSS split die are its wear resistance and toughness from M2 HSS, the adjustability and improved chip egress afforded by the split, and compatibility with standard BSW components. The black oxide finish option offers added protection against rust during storage and light use. For safe, accurate results use with a matched die stock and follow recommended cutting speeds and lubrication for HSS tooling.

Duchy Fasteners stocks a wide range of imperial dies and die nuts, including other BSW sizes and pack options; items are available singly or in economical multi-packs to suit workshop and trade requirements.