This product is a 1/2"-12 BSW split die manufactured in high‑speed steel (HSS) with a 1.1/2" (1.5") outer diameter, intended for cutting, restoring and sizing 1/2" BSW (British Standard Whitworth) external threads. Its primary use is to produce or repair the 55° Whitworth thread form on studs, bolts and shafts where the imperial 12 threads per inch (tpi) profile is required.

The die is produced from M2 high‑speed steel, offering excellent hot hardness and wear resistance compared with carbon or low‑alloy tool steels. The cutting edges are ground to a bright finish; as HSS is not stainless, a light coating of cutting oil is recommended during use to reduce friction and prevent surface oxidation. The thread form conforms to the Whitworth 55° profile (BSW) and the die will cut nominal 1/2"-12 threads (pitch 0.0833" / 2.1167 mm). As a split die it includes a small adjustment screw to open or close the cutting diameter slightly, which is useful for fine‑tuning fit or for chasing damaged threads.

This split die is suitable for both hand and machine applications: it can be mounted in a standard 1.5" die stock for manual threading or used in compatible die holders on production lathes and thread‑rolling setups where HSS dies are appropriate. Typical industries and applications include restoration and maintenance of classic British vehicles and motorcycles, agricultural and vintage machinery servicing, general engineering workshops, heritage rail and steam plant maintenance, and any situation requiring compatibility with BSW fasteners.

Key benefits include the M2 HSS material for longer tool life and easier re‑sharpening, the adjustability of the split design for precise thread fit or repair work, and direct compatibility with existing 1/2"-12 BSW fasteners and die stocks. While HSS offers superior cutting durability, regular lubrication and storage in a dry environment will prolong service life.

Duchy Fasteners holds a comprehensive range of hand and machine HSS taps and dies in imperial sizes; this 1/2-12 BSW split die is available individually and as part of boxed sets, with multiple pack options to suit workshop and trade requirements. Please contact us for specific size and pack availability.