The NES 1A, is a universal external thread repair tools and the NES21 and NES22 are internal thread repair tools. These easy-to-use tools operate by adjusting the knob that sets the proper diameter of the tool to the thread and the blades float to the correct pitch. Once the tool fits into a thread slot, begin repairing the threads by simply rotating the tool. Comes equipped with blades made from hardened steel. CONVENIENCE: universal thread repair tools require only one hand to repair inch or metric, right or left handed, coarse or fine threads VERSATILE: no need for a caliper or pitch gauge to determine diameter or thread count or type with the threaded sizing feature QUICK ADJUSTMENT: tool adjusts and quickly adapts to particular diameter and pitch of fastener thread DESIGN: automatically chases good threads and the cutter repairs damaged threads DURABILITY: blades are made of high speed steel induction hardened to 58 Rockwell for longevity of life UNIVERSAL TOOL: takes the place of hundreds of dies, assorted thread chasers and thread files and NES Internal thread restorers.Made in Israel