Vermont American 21987 8 Piece High Carbon Steel Rethreading Die Set The thread restoring file is used for renewing damaged external threads. Use to restore right- or left-handed threads on any diameter. Plastic storage case is constructed of sturdy, blow molded plastic. Includes the following: re-threading dies for sizes 1/4" NF, 5/16" NF, 3/8" NF, 7/16" NF, 1/2" NC, 9/16" NF, 5/8" NF and 3/4" NF threads.