This 1/2-20UNF (1"5/16) RH HSS split die is a round cutting die designed to cut or restore external Unified National Fine (UNF) threads on bars, studs and fasteners. Its primary use is for machining or hand-threading 1/2‑inch diameter parts to the 20 threads-per-inch UNF form, and for cleaning damaged or corroded threads to a controlled finish.

The die is manufactured from high-speed steel (commonly M2 grade HSS) with a bright ground finish and incorporates a radial split with an adjustment screw to permit slight size correction and relief for re-threading operations. The thread form is 1/2-20 UNF, right-hand, manufactured to the Unified thread standard (ANSI/ASME B1.1) and produced to industry tolerances suitable for general engineering and maintenance work. The die blank is sized to fit standard 1 5/16-inch round die stocks used in hand and machine holders.

Typical applications include workshop maintenance, engineering fabrication, automotive and motorsport repair, aerospace component refurbishment, plant maintenance and general manufacturing where UNF fine threads are required. The split design is particularly useful for restoring partially damaged threads, achieving a close fit on turned parts, and allowing controlled sizing when interfacing with precision fasteners.

Key benefits of this HSS split die are the wear resistance and edge-holding capability of M2 high-speed steel, which gives improved tool life compared with carbon steel alternatives. The split construction provides adjustable cutting clearance and reduces the risk of overcutting delicate components. While the bright HSS finish offers limited corrosion resistance, parts can be supplied with a black oxide treatment for enhanced rust protection where required. The die is compatible with standard die stocks and holders and is suitable for use on common materials such as mild steel, stainless steel (with appropriate lubrication), aluminium and brass.

Duchy Fasteners stocks this item (DIEF0050) across a range of imperial split dies and complementary die stocks. Sizes are available individually and in multi-pack options to suit workshop and production requirements. If you need a different finish or a matched die stock, please contact Duchy Fasteners for availability.