Steel Bit - 10pcs (4mm) pkt

A packet of ten 4mm twist drill bits for steel. Four millimetres is a size that gets used constantly rather than occasionally - clearance for M4 fixings, pop rivet holes, light brackets and cleats, trunking and enclosures - and buying ten means the drawer is never down to its last one when a run of holes comes up. Bits at this diameter are sturdier than the fine sizes and rarely snap outright; they simply go blunt, and a blunt bit rubs and work-hardens the steel instead of cutting it, which then defeats the next bit too. Change them earlier than feels necessary. Hammer action off, moderate speed, punch mark first, and cutting oil on anything thicker than sheet.