Century Drill Tool 92931 National Coarse Right Hand Rethreading Set, 7-Piece For repairing damaged threads on bolts or studs. Will not crosscut or undercut the thread the way a cutting die would. Do not use on hardened threads or to cut new threads. Made of high carbon alloy steel for a long tool life. Features Precision cut threads, accurately formed for consistent, exact rethreading For repairing damaged threads on bolts or studs Will not crosscut or undercut the threads as a cutting die would 7 piece National Coarse rethreading set includes 1/4" 5/16" 3/8" 7/16" 1/2" 9/16" and 5/8" National Coarse