These reamers are manufactured by CLYMER Precision using the best M42 w/ Cobalt HSS available. (Cobalt steel is more resistant to heat and abrasion than many other high-speed steels, which dramatically increases tools life and durability) Manufacturer grade tooling Smooth/free cutting guaranteed Live pilot spindle threaded for 4-40 fillister head screw to easily attach industry standard bushings (no C clips required) Oil grooves standard in pilot spindle to allow for muzzle flush chambering applications Industry standard 7/16" shank with integral Weldon flat and 1/4-28 female threads Live piloted reamers allow for customer to int Mfg: Clymer