Nicholson 4 Piece Thread Repair File Set, Single Cut, Square Shape, Fine, 8-3/8" Length Used to restore damaged or worn external threads on bolts, pipes Each thread restoring file will work with 8 different thread sizes Files are made in U.S.A. Available in 3 sizes and in a convenient 4-piece set Caps are color coded: 1=Black, 2=Red, 8=Blue Used to restore damage or worn external threads on bolts, pipes, etc. Each thread restoring file will work with 8 different thread sizes Convenient 4-piece set Color caps on tubes Type 1 black cap: Regular bolt; 11-12, 13-14, 16-18, 20-24 TPI Type 2 red cap: Ex. Fine/ex. Coarse bolt; 9-10, 12-16, 20-27, 28-32 TPI Type 7 green cap: Regular pipe; 8-10, 11 1/2-14, 16-18, 24-27 TPI