🔧 Product Review
Best Type of Drill Bit for Stainless Steel UK
Cobalt (HSS-Co) drill bits are the best type for stainless steel. The cobalt alloy keeps its hardness at the temperatures that soften plain HSS and titanium-coated bits, and it holds a cutting edge where cheaper bits rub, harden the surface and dull in seconds. We compared 5 cobalt sets sold in the UK, from a £30 Milwaukee that suits most workshops to Bosch's dedicated stainless line, and set out the slow-speed, cutting-fluid technique that decides how long any of them last.
Key Takeaways
- Cobalt (HSS-Co) is the best drill bit type for stainless steel. The cobalt alloy holds its hardness at the temperatures that soften plain HSS, which is why the Milwaukee Red Cobalt set is our top pick for most UK makers.
- Best premium pick: the Bosch PRO Stainless Steel HSS-Co set is designed specifically for stainless work, with 135° split-point tips and a proper ProBox case.
- Trade favourite: the Sealey AK4702 cobalt set holds a 4.5-star rating across about 4,700 Amazon ratings.
- Split points stop wander: the UK Drills 135° split-point cobalt set self-centres on curved stainless where standard 118° tips skate across the surface.
- Technique decides bit life. Slow speed, firm pressure and a splash of CT-90 cutting fluid matter as much as the bit you buy.
Suggested reading: Drill Bit Types Explained, Cordless Drill Torque Explained and Can You Use HSS Drill Bits on Masonry?
Quick Picks
🏆 Best Overall
Milwaukee HSS-G Red Cobalt 25-Piece Set
1-13mm, 5% cobalt, around £30
💎 Best Premium
Bosch PRO Stainless Steel HSS-Co 25-Piece Set
Dedicated stainless line, ProBox case
🔧 Best for Trade
Sealey AK4702 Metric Cobalt Set
4.5★ from about 4,700 ratings
🎯 Best Split Point
UK Drills 25-Piece Cobalt Set
135° split point, fully ground
🥈 Best for Mixed Metals
PTI 25-Piece Cobalt HSS Set
Iron, alloy steel and sheet metals too
Quick Comparison
| Product | Price* | Rating | Cobalt | Sizes | Best For |
|---|---|---|---|---|---|
| Milwaukee Red Cobalt 25pc | £29.92 | 4.7★ | 5%, DIN 338 | 1-13mm | Best overall value |
| PTI Cobalt HSS 25pc | £49.99 | 4.5★ | Cobalt HSS | 1-13mm | Mixed metals |
| UK Drills Cobalt 25pc | £55.00 | 4.5★ | Cobalt steel, 135° split | 1.0-13.0mm | Accuracy on curves |
| Sealey AK4702 25pc | £79.99 | 4.5★ | Cobalt | Metric range | Trade toolboxes |
| Bosch PRO HSS-Co 25pc | £89.99 | 4.7★ | 5%, Type N, h8 | 1-13mm | Frequent stainless work |
*Prices checked on Amazon UK on 23 August 2026 and they move around, so treat them as a guide.
In-Depth Reviews
1. Milwaukee HSS-G Red Cobalt Metal Drill Bit Set (25 Piece)
★★★★★ 4.7 on Amazon UK
£29.92 at the time of writing | 25 bits, 1-13mm in 0.5mm steps | 5% cobalt HSS, ground from solid to DIN 338
This is the set most people should buy for stainless. Milwaukee grinds these bits from solid 5% cobalt high-speed steel to DIN 338, and the listing rates them for steels above 1,000 N/mm², which covers the stainless grades you'll meet in the workshop, from 304 sheet to 316 bar. The cobalt alloy is mixed through the whole bit rather than sitting as a coating, so the cutting edge keeps its hardness as the bit wears.
What stands out is the price against the spec. Cobalt sets from the big brands often sit at £60 to £90, and this one undercuts them while carrying a 4.7-star Amazon rating. Amazon purchaser feedback consistently centres on the same theme: the bits cut hard steel cleanly where cheaper HSS sets gave up. For a full metric range covering everything from 1mm pilot work to 13mm holes at around thirty pounds, nothing else in this comparison matches the value.
✅ Pros
- 5% cobalt through the whole bit, not a coating
- Rated for steels over 1,000 N/mm² including stainless
- 4.7★ Amazon rating at a mid-budget price
- Full 1-13mm range in 0.5mm steps
❌ Cons
- 5% cobalt rather than the 8% on premium M42 bits
- Bits only, so budget for cutting fluid
2. Bosch 25x PRO Stainless Steel HSS-Co Twist Drill Bit Set
★★★★★ 4.7 on Amazon UK, from about 5,080 ratings
£89.99 at the time of writing | 25 bits, 1-13mm | 5% cobalt, DIN 338 Type N, 135° tips, h8 tolerance, ProBox case
Bosch sells this line with stainless in the product name, and the spec backs the label up. The bits are 5% cobalt HSS manufactured to DIN 338 in Type N geometry with 135° split-point tips and an h8 diameter tolerance, which is the tight tolerance that keeps hole sizes honest in metal. The set ships in a ProBox case that takes individual bits out without dumping the rest across the bench.
The 4.7-star rating across more than 5,000 Amazon ratings makes this the most heavily reviewed set in the comparison, and the consensus among purchasers is that the bits hold their edge through repeated stainless work where own-brand sets blunt after a few holes. At £89.99 it costs three times the Milwaukee, so it makes sense for people who drill stainless or other hard alloys regularly. If you drill the odd bracket a couple of times a year, the Milwaukee leaves you plenty of change. Bosch also recommends pairing the set with their cutting oil, and any decent cutting fluid does the same job.
✅ Pros
- Designed specifically for stainless steel
- 135° split points and h8 tolerance for accurate holes
- 4.7★ across roughly 5,080 ratings
- ProBox case keeps sizes organised
❌ Cons
- Premium price for occasional use
- Same 5% cobalt content as sets costing half as much
3. Sealey AK4702 Metric Cobalt Drill Bit Set (25 Piece)
★★★★☆ 4.5 on Amazon UK, from about 4,700 ratings
£79.99 at the time of writing | 25 cobalt bits, metric range | Trade-oriented brand with wide UK dealer support
Sealey is a fixture in UK workshops and garages, and the AK4702 is the cobalt set that turns up in trade toolboxes. The 4.5-star rating is built on roughly 4,700 Amazon ratings, which is serious volume for a trade-oriented bit set, and purchaser feedback tends to highlight bits that survive repeated work on hard materials. Sealey's UK dealer network matters too: if a set arrives with a problem, getting it sorted is straightforward.
Against the Milwaukee it costs fifty pounds more for a similar job, so the case for the Sealey rests on brand preference, dealer support and wanting your bit sets to match the rest of a Sealey-filled workshop. For anyone already running Sealey tool storage or hand tools, keeping the ecosystem consistent is worth something. The rating volume also suggests these have been bought in bulk by people who use them daily, which tells you more than any spec sheet.
✅ Pros
- 4.5★ from about 4,700 Amazon ratings
- UK trade brand with strong dealer support
- Proven daily-use track record
❌ Cons
- Costs £50 more than the Milwaukee for the same job
- Cobalt content not stated on the listing
4. UK Drills 25 Piece Cobalt Set (1.0mm to 13.0mm)
★★★★☆ 4.5 on Amazon UK
£55.00 at the time of writing | 25 bits, 1.0-13.0mm | Cobalt steel, fully ground, 135° split point
The headline feature here is the 135° split point on every bit. A split point self-centres as it starts cutting, which matters on stainless for two reasons: it stops the bit wandering across curved or rounded stock, and it cuts the pressure you need to start the hole, which in turn cuts the heat. Less heat means less work-hardening, which means your bit keeps cutting. The bits are fully ground cobalt steel, and the set covers 1.0mm to 13.0mm.
UK Drills is a British brand that manufactures to ISO and DIN standards, and the 4.5-star Amazon rating reflects steady purchaser satisfaction with the split-point performance in particular. At £55 this sits between the Milwaukee and the trade brands, and it earns its place if you drill a lot of rounded stainless tube, handrail or sheet that punishes standard tips. For flat plate work the split point matters less, and the Milwaukee does the same job for less money.
✅ Pros
- 135° split points on every bit reduce wander
- Fully ground cobalt steel
- British brand, manufactured to ISO and DIN standards
❌ Cons
- Split point premium is wasted on flat plate work
- Mid-price with no stand-out value angle
5. PTI 25-Piece Cobalt HSS Twist Drill Bit Set (1mm to 13mm)
★★★★☆ 4.5 on Amazon UK
£49.99 at the time of writing | 25 bits, 1-13mm | Cobalt HSS rated for steels over 800 N/mm²
The PTI set is rated for steels above 800 N/mm², which includes most stainless grades along with alloy steels and bearing steels, and the listing also covers iron, sheet metals and non-ferrous metals. That breadth makes it a sensible single-set answer if your metalwork jumps between stainless brackets, mild steel box section and the odd aluminium panel. Amazon purchasers rate it 4.5 stars, and the feedback consensus is that the cobalt bits handle hard steels respectably for the money.
It doesn't beat the Milwaukee on price or the Bosch on spec, and the cobalt percentage isn't stated on the listing, which is a gap next to the fully specified sets above. But as a general workshop metal set that copes with stainless when it turns up, rather than a set dedicated to it, the PTI covers the widest range of jobs per pound in this comparison. If stainless is a regular material for you, pick a set that names its cobalt content instead.
✅ Pros
- Rated for steels over 800 N/mm² including stainless
- Covers iron, alloy steel, sheet and non-ferrous metals
- 4.5★ Amazon rating
❌ Cons
- Cobalt percentage not published on the listing
- Generalist set, not stainless-dedicated
How to Choose a Drill Bit for Stainless Steel
Start with cobalt. Stainless steel is tough, and it work-hardens the instant a bit rubs against it without cutting. That rubbing heat softens the tip of a plain carbon or standard HSS bit, the bit stops cutting, and every second it spins without biting makes the surface under it harder. Cobalt high-speed steel, usually 5% cobalt in the M35 class, keeps its hardness at temperatures that would soften ordinary HSS, which is exactly why every serious answer to the stainless question starts with HSS-Co. Our guide to drill bit types covers where cobalt sits among the full range.
Check the cobalt is alloyed, not coated. A titanium-nitride coated HSS bit looks the part, but the coating sits on a softer core. Coated bits cope with thin stainless sheet and a handful of holes, then the coating wears at the cutting edge and the soft core underneath dulls fast. Cobalt bits are the same alloy all the way through, so they keep cutting as they wear. If a listing shouts "titanium" but never states a cobalt percentage, it's the wrong bit for repeated stainless work.
Look for 135° split points and ground flutes. A split point tip self-centres and needs less pressure to start the hole, which means less heat on curved surfaces. Ground flutes, where the bit is machined from solid rather than rolled, cut more cleanly and run truer. DIN 338 on the listing tells you the bits follow the standard jobber dimensions, and an h8 diameter tolerance means the holes come out the size printed on the tin.
Match the set to how often you drill metal. If stainless shows up in your projects monthly or more, a dedicated cobalt set pays for itself in bits you don't ruin. If it's an occasional bracket, the Milwaukee covers it without a premium outlay. For a broader spread of bit types beyond metal work, our roundup of the best drill bit sets UK covers the multi-material options, and if you've ever wondered whether those same HSS bits belong near brickwork, we tackled that question in can you use HSS drill bits on masonry.
The Technique Matters as Much as the Bit
A £90 cobalt set drilled dry at full throttle will dull as fast as a budget set used properly. Stainless rewards patience with three habits.
Run slow. Heat is the enemy, and speed makes heat. As a working guide, keep a 3mm bit under roughly 1,000 RPM and a 6mm bit under about 500 RPM, which on a cordless drill means selecting the low gear. Low gear also multiplies torque, and our explainer on what drill torque numbers mean covers why that pairing matters. If the swarf coming off the bit turns straw or blue, you're running too hot and hardening the hole as you go.
Use cutting fluid. A few drops of Action Can CT-90 cutting and tapping fluid carries heat away from the cutting edge and stops chips welding themselves to the flutes. Dry drilling is the single fastest way to kill a bit in stainless, and a 500ml bottle costs less than one decent cobalt bit. Add fluid at the start of the hole and top up as you go.
Push steadily and keep the bit cutting. A light touch lets the bit rub, and rubbing is what work-hardens stainless. Apply firm, consistent pressure so the cutting edges bite and produce chips, ease off only to peck the bit clear of chips in deeper holes, and never let a spinning bit sit in the hole without feeding. For larger holes above about 8mm, start with a pilot hole around 3mm and step up, which spreads the work across two bits instead of overloading one. The same steady-pressure principle applies when you're drilling through metal studs behind drywall.
Frequently Asked Questions
Final Verdict
For most UK makers, the Milwaukee HSS-G Red Cobalt 25-piece set is the right answer to the stainless steel question. It puts genuine 5% cobalt, ground to DIN 338 and rated for steels over 1,000 N/mm², in a full 1-13mm range at around £30, with a 4.7-star rating behind it. Buy it, pair it with cutting fluid, run it slow, and it will drill stainless all day.
If you drill stainless weekly, step up to the Bosch PRO Stainless Steel HSS-Co set, which adds split points, h8 tolerance and a case built for daily bench work. Trade users already invested in Sealey will be happy with the AK4702, and the UK Drills split-point set earns its keep on curved stock. Whichever set you choose, the bit is only half the job: slow speed, firm pressure and CT-90 cutting fluid are what keep any of them cutting.
Last reviewed: 23 August 2026 · Evidence-based review · Contains affiliate links