HSS M2 grade woodruff Hardened keyseat cutter Set of 10 Pcs in 1/2" Shank diameter.Straight tooth cutters Dimensions as Dia x Thickness: STD 403: 3/8" x 1/2", STD 204: 1/2" x 1/16", STD 404: 1/2" x 1/8", STD 305: 5/8" x 3/32", STD 505: 5/8" x 5/32" STD 406: 3/4" x 1/8", STD 606: 3/4" x 3/16", STD 806: 3/4" x 1/4", STD 608: 1" x 3/16", STD 808: 1" x 1/4" Used to make a groove or slot, which serves as a seat for a complementary engagement key. They are typically used in key shafts to provide positive engagement and prevent unwanted rotation or movement.