Its sturdy Bearing Steel and 40Cr Mold Steel material are strong and sturdy enough to ensure durability for long lifespan. Your comprehensive toolkit for every rethreading need! 7 x Unified Fine(UNF) Thread Dies (Black): 1/4"-28, 5/16"-24, 3/8"-24, 7/16"-20, 1/2"-20, 9/16"-18, 5/8"-18.