What is the best drill bit for stainless steel?

A cobalt bit. M35 cobalt (5 percent) handles most stainless, and M42 cobalt (8 percent) lasts longer again on tougher grades and repeat work. Plain HSS will drill stainless but blunts quickly because stainless work-hardens and generates heat.

Can I use an HSS bit on stainless steel?

You can, but it won't last. Standard HSS loses its edge quickly against stainless. It is fine for the odd hole if you go slow with fluid, but for anything more, cobalt is far more forgiving and much longer-lasting.

How to Drill Stainless Steel Without Ruining the Bit

Q: What speed should I drill stainless steel?

Slow, roughly half the speed of mild steel. About 650 RPM for a 6 mm bit, 500 RPM for 8 mm and 400 RPM for 10 mm. The key is to keep the bit cutting rather than rubbing, so pair the low speed with firm, constant pressure and cutting fluid.

Q: Why can't I drill through stainless steel?

Almost always because the surface has work-hardened. Drilling too fast, or letting the bit spin without cutting, glazes the stainless glass-hard and the bit then skates on it. Slow right down, use firm pressure so it is always cutting, add cutting fluid, and use a sharp cobalt bit.

Q: Do I need cutting fluid to drill stainless?

Yes, in practice. Stainless generates a lot of heat and cutting fluid carries it away, keeps the edge sharp and stops the surface work-hardening. It makes the difference between one clean hole and a burnt-out bit.

October 1, 2026

The one thing to understand:

Stainless work-hardens — so the bit must always be cutting, never rubbing.

Slow speed (about half mild steel), firm constant pressure, cutting fluid and a sharp cobalt bit. Let it spin without biting for a second and the surface glazes glass-hard.

Stainless steel is the material that convinces people their drill bit is faulty. It isn’t — stainless just behaves differently to mild steel. Get the technique right and it drills cleanly. Get it wrong and you’ll blunt a bit on a single hole. Here’s how to get it right.

Why stainless wrecks drill bits

Stainless steel work-hardens: the act of working it makes it harder. Drill too fast, or let the bit rub instead of cut, and the friction hardens the surface into a glassy skin that the bit can no longer bite into. From there it just spins, generates more heat, and the edge burns off. Nearly every “this bit is rubbish” story on stainless comes back to this one thing.

The five rules for drilling stainless

Go slow. Roughly half the speed you’d use for mild steel. High revs are the number-one cause of work-hardening. See our drill speed chart for figures.

Firm, constant pressure. Lean into it enough that the bit is always cutting a chip. A bit that’s skating is a bit that’s hardening the surface.

Use cutting fluid. Not optional. It carries away heat, keeps the edge sharp and stops the surface glazing. A proper cutting compound or even a general lubricant beats drilling dry every time.

Use a sharp cobalt bit. M35 cobalt for most stainless, M42 for tougher grades and repeat work. Cobalt keeps its edge at the heat stainless throws off. (More on why in our cobalt vs HSS guide.)

Don’t dwell. Get in, cut, and don’t let the bit ride on the spot without advancing. For bigger holes, drill a pilot first so the main bit isn’t fighting its own chisel point.

Speeds for stainless

Bit size	Stainless	(Mild steel)
4 mm	950	2250
6 mm	650	1500
8 mm	500	1100
10 mm	400	900
12 mm	300	750

Speeds in RPM, starting points for a cobalt bit. Most cordless and hand drills top out around 2,500–3,000 RPM, so for stainless you want a low gear or a variable trigger held right back.

If it’s already work-hardened

Hit a glazed, shiny spot that won’t cut? Don’t just push harder on the same place — you’ll only polish it. Options:

Move to fresh metal a few millimetres over if the position allows.
Grind or file through the hardened skin to expose softer material underneath, then drill slowly with fluid.
Step up to a sharp M42 cobalt bit, very slow, heavy pressure, and don’t let it stop cutting once it bites.

Cobalt built for stainless — from stock

M35 and M42 cobalt in single sizes and sets, dispatched the same day. Free next-working-day UK delivery on orders over £50.

M35 cobalt · M42 cobalt · Drill speed chart

Frequently asked questions

What speed should I drill stainless steel?

Slow — roughly half the speed of mild steel. About 650 RPM for a 6 mm bit, 500 RPM for 8 mm, 400 RPM for 10 mm. Pair the low speed with firm pressure and cutting fluid so the bit keeps cutting.

What’s the best drill bit for stainless steel?

A cobalt bit. M35 (5% cobalt) for most stainless, M42 (8%) for tougher grades and repeat work. Cobalt holds its edge at the heat stainless generates; plain HSS blunts quickly.

Why can’t I drill through stainless steel?

The surface has almost certainly work-hardened. Too much speed or a rubbing bit glazes stainless glass-hard. Slow down, keep firm pressure so it’s always cutting, use fluid, and reach for a sharp cobalt bit.

Do I need cutting fluid to drill stainless?

In practice, yes. It carries away heat, protects the edge and stops the surface hardening — the difference between a clean hole and a burnt-out bit.

Can I use an HSS bit on stainless?

You can for the odd hole, going slow with fluid, but it won’t last. For anything more, cobalt is far more forgiving.

UK Drills has supplied drill bits to UK trade and industry since 1985, from our trade counter in Hindley, Wigan. Not sure what you need? Email info@ukdrills.com — we’re happy to advise.