This is a 5/16-18 UNC right‑hand split round die, 1" diameter, designed for cutting or restoring external Unified Coarse (UNC) threads on rods, studs and shafts. Its primary use is to produce or refurbish 5/16" diameter, 18 threads‑per‑inch external threads where a standard UNC profile is required, and the split design allows fine adjustment of the finished thread form for either free‑running or tighter fits.

The die is manufactured from high‑speed steel (HSS), typically M2 grade, giving good hot‑hardness and edge retention for general workshop use. The body is supplied in a bright, ground finish and is supplied as a single‑split die with an adjustment screw to change the effective cutting diameter. Thread form and pitch conform to the Unified thread specification (5/16‑18 UNC, 18 tpi) as defined in ANSI/ASME B1.1, producing a standard right‑hand, external thread to mate with corresponding UNC bolts and nuts. The die requires a compatible 1" round die stock (holder) for safe, controlled cutting and drive; it is not intended for use in powered die stocks unless specifically rated for such use by the holder manufacturer.

Typical applications include general engineering workshops, maintenance and repair operations, automotive and agricultural machinery repair, fabrication and plant maintenance where imperial UNC fasteners are used. The tool is suitable for machining mild steel, free‑cutting steels, brass, aluminium and plastics; it is not recommended for hardened steels without specialist grades or coatings.

Key benefits include the wear resistance and thermal stability of M2 HSS for reliable cutting performance, the adjustability of the split design to correct minor thread distortion or to achieve specific fit classes, and compatibility with standard UNC fasteners. Note that bright HSS is not inherently corrosion‑resistant; light oiling after use and dry storage will reduce rusting. For improved corrosion protection, black oxide or other coated versions may be used where available.

Duchy Fasteners stocks a wide range of hand and machine dies, including split and solid types in common imperial and metric sizes, die stocks and holders. This item is sold under code DIEC0031 and is available individually or in assorted packs to suit workshop and maintenance requirements. Contact Duchy Fasteners for available sizes and pack quantities.