Heller prefix hss metal drill bits heller 27422 7 this prefix universal drill bit from heller is a reliable metal drill bit ideal for unalloyed steel and non ferrous metal this 55 x 57 x 93mm bit has a web thinned centre point for accurate bit positioning supplied in packs of 2 heller 27422 7 0911 prefix hss metal drill bit 55 x 57 x 93mm pack of 2