Used to restore damaged 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 Type 8 blue cap: Metric Bolt; .75-1.0, 1.25-1.5, 1.75-2.0, 2.5-3.0 mm