UNC (Unified National Coarse) Chrome Alloy Hand TapsThis thread form was introduced in 1948 as an attempt to standardise thread forms in the USA, Canada and the UK. The thread profile of UNC is the same as for metric threads and is described in the JIS B0206 standard. The thread is described by its major diameter and the number of threads per inch of length (TPI). This thread series is commonly used in the mass production of bolts, screws and nuts. It is used for threading into lower tensile strength materials (bronze, brass, aluminium and plastics) to obtain the best resistance to stripping of the internal thread. It is also used on quick assembly or disassembly or if corrosion or slight damage is possible.Taper Taps have a lead of eight threads and are used as a starting tap in difficult or high precision holes. Manufactured from premium chrome alloy steel this general purpose tap is designed for use in medium tensile materials and is for hand or general machine use.