Thin sheet metal grabs a standard twist bit, punches through suddenly, and leaves torn, triangular holes with a razor burr. The best drill bits for sheet metal are step bits for clean round holes, or sharp cobalt twist bits for thicker gauge. Here is how to choose the right one for the job.
What to Look For
The problem with sheet metal is not hardness — it is that a normal bit bites through before the full diameter is cut, snagging and deforming the thin material into a three-cornered hole. Step bits solve this by cutting progressively larger circles as they advance, so the hole stays round and the burr stays small. One step bit also covers a whole range of hole sizes, which is handy for electrical and HVAC work. For thicker plate and stainless sheet, a cobalt twist bit with a sharp split point resists the heat and holds its edge. Always back thin sheet with a scrap of wood to stop it flexing and tearing.
The Best Type of Bit for Sheet Metal
For thin sheet and multiple hole sizes, a step bit is ideal — one bit drills a range of clean, round, low-burr holes without grabbing. For heavier gauge, mild steel plate and stainless sheet, choose a cobalt twist bit with a 135° split point.
- Thin sheet: Step bit for round, low-burr holes and no snagging.
- Thicker gauge: Cobalt twist bit with a 135° split point.
- Backing: Clamp scrap wood behind the sheet to stop tearing and flex.
- Speed: Moderate speed with light feed keeps the edge from grabbing.
Technique and Mistakes to Avoid
Clamp the work so it cannot spin — a loose sheet that catches the bit becomes a spinning blade and instantly ruins the hole. Ease off pressure as the bit breaks through, since that is the moment a twist bit snatches most. Use cutting oil on steel and stainless sheet, and go dry with light pressure on aluminium. Deburr afterwards for a clean, safe edge, and pick your hole size before you start so a step bit stops at the right diameter. Our USA-made cobalt bits and drill sets handle sheet metal from aluminium to stainless.
Matching the Bit to the Gauge
Thin gauges under about 1.5 millimetres are where step bits shine, giving round holes without a pilot. As the sheet gets thicker and starts to behave like plate, a twist bit becomes the better tool because a step bit would leave a long taper. For larger diameters in thin sheet, a hole saw or a step bit sized to your knockout keeps the edge clean. Whichever you use, match the finished hole to the fastener or grommet you are fitting so it seats snugly and looks tidy.