This 9/16" BSW (1 5/16) RH HSS split die is a precision-cutting tool designed to cut, restore or reform external BSW (British Standard Whitworth) threads on bolts, studs and bar stock. Its primary use is in the hand or machine rethreading of Whitworth fasteners where adjustable control is required to correct damaged threads or to cut new threads to the BSW form.

The die is manufactured from M2 high-speed steel (HSS) and is supplied with a black oxide finish to reduce light surface corrosion and aid chip flow. It is a right-hand (RH) die manufactured to the Whitworth 55° thread form in accordance with BS 84 (British Standard Whitworth thread form). The split design incorporates a longitudinal slot and an adjustment/set screw so the effective cutting diameter can be closed or opened slightly for fine adjustment or to compensate for worn material and plating thickness. The die is compatible with standard round die stocks and machine die holders designed for Imperial split dies.

Typical applications include workshop maintenance, heritage and classic vehicle restoration, agricultural and marine repair where Whitworth fasteners are still in service, and general engineering where legacy equipment uses Imperial Whitworth threads. The M2 HSS material gives improved hot hardness and edge retention compared with carbon-steel dies, allowing cleaner cuts and longer life when working on mild steel, low-alloy steels, brass or bronze. Use appropriate cutting fluid and controlled feed rates when cutting harder materials or stainless steels.

Key benefits of this split die include the ability to adjust cutting action for finishing or reclaiming threads, the wear resistance and heat tolerance of M2 HSS, and the corrosion resistance afforded by the black oxide finish. Its compatibility with standard die stocks and adherence to the BSW/BS 84 form ensure interchangeability with existing Whitworth hardware.

Duchy Fasteners stocks this 9/16" BSW RH HSS split die individually and as part of complementary sets; we also carry other BSW sizes, matching die holders and taps in single units and multi-pack configurations for workshop or site use.