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Cobalt vs HSS drill bits

Updated: October 2026

You already own a plain HSS set, or you are looking at a black-and-gold box, and you want to know whether cobalt is the bit for stainless. Shop guides say HSS fails on stainless. The British Stainless Steel Association says standard HSS is suitable if it is sharp and preferably short. Copying only one sentence sends you to the wrong box. This page is the cobalt vs HSS drill bits fork. Prices stay on the [stainless steel drill bit comparison](/hub/drilling-and-accessories/stainless-steel-drill-bit). Products Compared set the ten amazon.co.uk listings from 15 October 2026 against those two sources, with no lab test. A qualifying purchase can earn a commission at no extra cost to you.

You already own a plain HSS set, or you are looking at a black-and-gold box, and you want to know whether cobalt is the bit for stainless. Shop guides say HSS fails on stainless.

Our top picks

Bosch Bosch PRO HSS-Co set, 19 pieces, 1–10 mm

Best overall

Bosch Bosch PRO HSS-Co set, 19 pieces, 1–10 mm
8.4/10about £34.52
View offer
Bosch Bosch HSS PointTeQ 18-piece metal set

Alternative

Bosch Bosch HSS PointTeQ 18-piece metal set
5.6/10about £11.95
View offer
Rennie Tool Company Rennie Tools 5-piece cobalt set, 4–10 mm

Best value

Rennie Tool Company Rennie Tools 5-piece cobalt set, 4–10 mm
8.3/10about £13.99
View offer
On this page
  1. 1.Two true sentences, not one slogan
  2. 2.HSS, HSS-G, HSS-Co and a coat
  3. 3.When you stay with HSS, and when you step up
  4. 4.Which listing is which

Two true sentences, not one slogan

BSSA says standard HSS is suitable for stainless if it is sharp, preferably short, with a 135° point, and if you do not let it dwell. A cobalt bit can still polish a hole into a hard skin. UK Drills points cobalt at stainless and cast iron, and HSS at mild steel, and warns that cobalt is more brittle. Its “several times longer” line is shop wording. These files do not contain that test. M35 is the about-5% grade for everyday 304 and 316. M42, about 8%, is absent from these ten listings. Sharp HSS can drill stainless, and a listing that says M35 or HSS-Co is the cobalt side when you keep the feed up.

HSS, HSS-G, HSS-Co and a coat

HSS is high speed steel, which is PointTeQ, with no cobalt added. HSS-G, in Thürmer’s glossary, means ground after hardening, not a cobalt percentage. HSS-Co means cobalt is in the steel. Bosch PRO does not print 5% or 8%. Several Greywolf bullets do. Irwin says a cobalt alloy remains after the gold is ground off, and a titanium nitride coat does not. The £60.79 Greywolf set is black and gold oxide and is labelled HSS-G.
Bosch Bosch PRO HSS-Co set, 19 pieces, 1–10 mm

Testsieger

Bosch Bosch PRO HSS-Co set, 19 pieces, 1–10 mm
8.4/10about £34.52
View offer

When you stay with HSS, and when you step up

Stay with plain HSS for mild steel, roofing sheet and galvanised sheet when you can keep a sensible speed. One UK buyer says PointTeQ was the wrong set for stainless, which matches a listing that never claimed it. Step up to M35 or HSS-Co for 304 or 316 if you can keep a chip forming. Rennie’s reviews describe that on one five-piece set, not as a lab ranking. Long or blue-tipped HSS is outside BSSA’s allowance. Speed, oil and pecking are on the how to drill page.

Which listing is which

PointTeQ, B076F43HPH, at £11.95 is the HSS side: 4.5 from 4,044 ratings, stainless absent. Bosch PRO, B009CGDSYI, at £34.52 is HSS-Co, percentage unstated, 135° centre point, every half millimetre from 1 mm to 10 mm including 7 mm, 4.6 from 5,129 ratings. Those reviews also cover mild steel and lintels. They are not the HSS side of the fork. Greywolf B0DZNQZK1V (£35.90) and B0DZNTPX51 (£34.99) say M35 and omit 7.0 mm. Rennie at £13.99 is M35 in five sizes. B0DZWRGDQQ at £60.79 is HSS-G, not a cobalt upgrade. If you drill 304 or 316, buy a listing that says M35 or HSS-Co and confirm the diameter is printed.

Common questions

Can ordinary HSS drill stainless steel?
BSSA says standard HSS drills are suitable, preferably shorter, with a 135° point, provided you do not let the bit dwell and rub. Shop guides still point you at cobalt for 304 and 316. Both can be true of different bits: a sharp short HSS bit on a careful feed, and a blunt HSS bit that polishes the surface. The PointTeQ listing does not claim stainless, and one UK review says it was the wrong set for that job.
What does M35 add that HSS does not?
M35 is the shop name for high speed steel with about 5% cobalt, sold for the heat of stainless and cast iron. The addition is cobalt in the steel, which is the claim on the Greywolf M35 bullets and on Rennie’s listing. Bosch PRO says HSS-Co and leaves the percentage off the page. UK Drills’ “several times longer” line is their wording. These files do not measure a life multiple.
Is a gold or black-and-gold bit cobalt?
Colour is a finish. The £60.79 Greywolf set is black and gold oxide and is labelled HSS-G, which Thürmer defines as ground after hardening. Irwin says a cobalt alloy remains after the gold is ground off, and a titanium nitride coat does not. Grevosea prints Titanium in the finish field beside an M35 claim. Read the material line before you pay for the colour.
Is M42 on this shelf?
M42 is the higher-cobalt grade, about 8% in UK Drills’ comparison with M35, aimed at harder production work and described there as more brittle. None of these ten amazon.co.uk listings is sold as M42. For ordinary 304 and 316, the cobalt-style choice on this shelf is a listing that says M35 or HSS-Co. Buying M42 means a different product from these ASINs.
Are cobalt bits more likely to snap?
Shop guides warn that cobalt is harder and less forgiving of side load. UK reviews on this shelf do include snapped small bits, on M35 sets and on plain HSS. A Greywolf review describes 2 mm and 3 mm bits breaking in a drill press at low revs. That fits a thin edge under bending. It does not isolate the alloy as the cause. Keep side load off 1–3 mm bits whichever grade you chuck.

Related pages

Cobalt drill bit set for stainless steel

Best drill bits for stainless steel

Drill bit for stainless steel sheet

Stainless steel drill bits

How to drill stainless steel: speeds, feed and oil

Sources

Public UK sources and the amazon.co.uk listings captured on 15 October 2026. The 8–12 m/min cutting-speed band is a rule of thumb, not a British standard.

  1. British Stainless Steel Association — Speeds and feeds for drilling and reaming stainless steels (retrieved 15 October 2026)
  2. Health and Safety Executive — PUWER overview (retrieved 15 October 2026)
  3. Health and Safety Executive — Using the right type of PPE (retrieved 15 October 2026)
  4. legislation.gov.uk — Consumer Rights Act 2015 (retrieved 15 October 2026)
  5. Armeg — Twister impact-rated HSS cobalt drill bits (retrieved 15 October 2026)
  6. Dormer Pramet A777 — jobber drill data sheet (BS 328, DIN 338, ISO 235) (retrieved 15 October 2026)
  7. David Harries — cobalt drill technical sheet (retrieved 15 October 2026)
  8. Thürmer Tools — drill FAQ (8–12 m/min is a rule of thumb, not a British standard) (retrieved 15 October 2026)