This product is a 3/8" BSW (British Standard Whitworth) right‑hand split die with a 1" (approx. 25 mm) die body diameter, designed to cut, restore or chase external Whitworth threads on studs and bolts. The split design allows the user to close or open the die slightly for a freer or tighter fit, making it ideal for cleaning up damaged threads or achieving an exact clearance on assembled components.

The die is manufactured from high speed steel (HSS), typically M2 grade, delivering wear resistance and the ability to maintain a cutting edge at elevated temperatures. It is supplied in a bright ground finish; light lubricants or cutting oil are recommended in use to assist chip evacuation and reduce wear. The thread form is Whitworth (55° thread angle with rounded roots and crests) manufactured to Whitworth specification (BS 84) for compatibility with BSW fasteners. This item is a right‑hand (RH) thread and is intended for imperial Whitworth sizes rather than ISO metric or UNC/UNF forms.

Designed for use in a hand die stock (standard die holders) and suitable for light machine work in appropriate holders at low spindle speeds, this split die will cut external threads in mild steel, alloy steels, brass, bronze and aluminium when used with correct lubrication and cutting speeds. With careful technique it can also be used to touch up stainless steel threads, though slower feeds and frequent lubrication are required.

Typical applications include general engineering maintenance, heritage and vintage vehicle restoration, agricultural and plant repairs, ship and marine maintenance where original Whitworth fasteners remain in use, and workshop preparation of replacement studs and bolts. The key benefits of a HSS split die are improved cutting life compared with carbon tool steels, the ability to fine‑tune thread fit due to the split, and broad material compatibility when used with correct cutting fluids.

Duchy Fasteners holds a wide range of imperial Whitworth split dies and die sets. Sizes are available individually and in multi‑pack options; please contact us for current stock levels, available sizes and packaging quantities.