Heller prefix hss metal drill bits heller 27425 8 this prefix universal drill bit from heller is a reliable metal drill bit ideal for unalloyed steel and non ferrous metal this 7 x 69 x 109mm bit has a web thinned centre point for accurate bit positioning supplied singly heller 27425 8 0911 prefix hss metal drill bit 70 x 69 x 109mm