Heller prefix hss metal drill bits heller 27415 9 this prefix universal drill bit from heller is a reliable metal drill bit ideal for unalloyed steel and non ferrous metal this 2 x 24 x 49mm bit has a web thinned centre point for accurate bit positioning supplied in packs of 2 heller 27415 9 0911 prefix hss metal drill bit 20 x 24 x 49mm pack of 3