Heller hss co cobalt twist drills din 338 rn heller 21294 6 these 53mm hss co cobalt twist drills from heller are equipped to tackle the toughest drilling jobs in stainless steel and metal they are made from a special hss steel with a 5 cobalt content sold in packs of 10 heller 21294 6 0990 hss co cobalt twist drills din 338 rn 53mm pack of 10