Heller hss co cobalt twist drills din 338 rn heller 21221 2 this 1mm hss co cobalt twist drill from heller is equipped to tackle the toughest drilling jobs in stainless steel and metal it is made from a special hss steel with a 5 cobalt content sold singly heller 21221 2 0990 hss co cobalt twist drill din 338 rn 10mm single