Die Set, 1/4 - 3/4" Rethreading, Hexagonal 5919  (Discontinued) 

For rethreading rusty or worn threads

Sizes include:one each of 1/4~20, 5/16~18, 3/8~16, 7/16~14, 1/2~13, 9/16~12, 5/8~11 & 3/4~10.