This is a No.4‑UNC (13/16) right‑hand split die manufactured from high speed steel (HSS) for cutting or restoring external Unified coarse (UNC) threads. Its primary use is forming or repairing external threads on bolts, studs and bar stock, either by hand in a die stock or fitted in a machine die holder for light production or maintenance work.

The die is produced from M2 high speed steel with a precision ground cutting face and a protective black oxide finish to reduce flash corrosion and improve chip evacuation. It is a split (adjustable) round die, sized and marked No.4‑UNC (13/16) RH, and conforms to the Unified Thread Standard (UNC) tolerances as defined in ANSI/ASME B1.1, making it compatible with standard UNC fasteners. The split design permits slight size adjustment for cutting or cleaning up worn threads and allows for easier removal. The die is intended for use in a standard round die stock or compatible machine holder; there is no separate head or drive — the tool is clamped in the holder and rotated to form the thread.

Typical applications include workshop maintenance, assembly and repair of electrical enclosures, instrumentation, light engineering components, timber and furniture fasteners, and where imperial UNC fasteners are used. Industries that commonly use split dies include mechanical engineering, automotive maintenance, marine repair, HVAC installation and general fabrication, particularly where occasional thread repair or mixed material work is required.

Key benefits of this M2 HSS split die are its hardness retention and wear resistance at elevated cutting temperatures, the ability to adjust the cut for reconditioning threads, and broad material compatibility: it will cut or clean threads in mild steels, alloy steels, brass, bronze, aluminium and many plastics (avoid hardened steels above approximately HRC 60). The black oxide finish gives modest corrosion protection and helps reduce galling during use; always use appropriate cutting fluid for best results.

Duchy Fasteners stocks a comprehensive range of HSS split dies and die stocks across imperial and metric sizes. This item is available in single pieces and small multi‑packs — please contact us for current sizes, pack quantities and availability.