HSS, 4 cutters Ø 15/64", 9/32", 5/16" and 13/32" (6, 7, 8 and 10mm). Four flute design. Supplied in wooden box. Proxxon milling and cutting 4-piece set. Contains: 15/64, 9/32, 5/16, 13/32-Inch (6, 7, 8 and 10mm).