Heller prefix hss metal drill bits heller 27416 6 this prefix universal drill bit from heller is a reliable metal drill bit ideal for unalloyed steel and non ferrous metal this 25 x 30 x 57mm bit has a web thinned centre point for accurate bit positioning supplied in packs of 2 heller 27416 6 0911 prefix hss metal drill bit 25 x 30 x 57mm pack of 2