CORTOOL inch Cobalt Drill Bits (20Pcs), M35 HSS Metal Jobber
✅ PROS
- M35 cobalt construction handles stainless steel and hardened alloys without glazing
- Full 20-piece fractional set (1/16 inch to 1/2 inch ) covers most shop and automotive jobs
- 135° split point starts on contact — no wandering, no center punching required
❌ CONS
- No metric sizes included; fractional-only limits international DIY users
- Thin plastic case doesn't hold bits snugly — expect to sort them after a drop
The Verdict
If you’ve ever watched a cheap HSS bit smoke out halfway through a single hole in 3/16" steel, you know the drill-bit frustration loop. It’s why the CORTOOL 20-piece M35 cobalt set earns its 4.6-star rating from 229 buyers — this is the set that stops the cycle. Cobalt doesn’t just cut; it survives. And at this price point, the value proposition is hard to argue with.
What you actually get
The box contains 20 jobber-length twist bits in fractional sizes from 1/16" up to 1/2", with the most-used mid-range sizes (1/8", 3/16", 1/4", 5/16", 3/8") doubled up so you don’t have to reorder mid-project. Each bit is M35 high-speed steel with 5% cobalt content — that’s the key spec. It’s not the cheaper M2 steel most budget sets use; M35 holds its edge at higher temperatures, which is exactly what you need when drilling stainless, cast iron, or hardened steel. The 135° split point is another pro-grade touch. Standard drill points wander on curved surfaces; this one bites immediately.
Real-world performance
I tested these on a mix of mild steel plate, a stainless steel sink flange, and some mystery-metal brackets from a salvage yard. Running at moderate RPM with cutting fluid, the 1/4" bit chewed through the steel plate cleanly, producing proper spiral chips rather than dust — a sign the geometry is cutting, not scraping. The stainless was slower going, but the bit stayed sharp through four holes, which is where typical HSS bits give up. One buyer put it plainly: “Used on 1/4” steel plate and it drilled like butter. The split point is no joke — no walking, no pilot holes needed."
Multiple reviewers mention these bits survived drill press and hand-drill abuse that killed their previous sets. The flutes are polished, which helps chip evacuation — less binding in deeper holes. For a hobbyist with an automotive project or a homeowner with a metal gate to fix, this set is genuinely enough.
Where it falls short
Let’s be honest about the gaps. First, no metric sizes — if you’re working on European cars or imported machinery, you’ll need a separate set. Second, the case is functional but forgettable. It’s a thin plastic holder with friction slots, not a molded latch case. One reviewer noted: “Dropped it off the workbench and now I’m sorting 20 individual bits by eye. It’s the only cheap-feeling part of this product.” Third, the 1/2" bit is the only one in that size — if you’re doing heavy structural work regularly, buy a dedicated 1/2" or 9/16" separately.
Who should buy these
This set is perfect for the home mechanic, the garage fabricator, or the DIYer who’s tired of replacing cheap bits every other month. It’s also a solid choice for a beginner metalworker — the split point reduces the learning curve. Skip it if you primarily drill wood (you’ll overpay for cobalt) or if you need metric sizing. Professional shops running production volume will want individual premium bits in specific sizes rather than a mixed set.
FAQ
Can these drill hardened steel or rebar?
M35 cobalt handles mild steel, stainless, and cast iron well. Rebar and hardened tool steel will still eat them — use carbide for that.
Do I need cutting fluid?
Not strictly, but it extends bit life dramatically, especially on stainless. Use any cutting oil or even motor oil in a pinch.
Are these bright finish or black oxide?
They’re bright polished with a gold-ish sheen from the cobalt content. They’ll show rust if left wet — wipe them down after use.
The Verdict
Buy it if you’re tired of burning through cheap bits on metal projects and want a set that actually lasts. The M35 cobalt composition and split-point geometry punch well above the price class.
Skip it if you need metric sizes, or if your metalwork is limited to occasional soft aluminum — you’ll save money with standard HSS.
Rating: 4.6/5 — Deducting half a star for the flimsy case and missing metric options. The bits themselves earn every bit of the praise.
Where to Buy
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Last updated: 2026-08-06. Ratings and prices current as of review date. Verify on Amazon before purchasing.