Selection Guide

HSS, Cobalt or Carbide: Which Drill Bit for Which Job

HSS 4241, M2, M35, M42, TiN-coated, solid carbide — six grades, real differences, and the honest answer to which one is worth the money for each material.

Xiaoman Tools Technical Team 17 Jun 2026 Updated 22 Jul 2026 4 min read

HSS, Cobalt or Carbide: Which Drill Bit for Which Job

Two drill bits can look identical, cost three times different, and one will drill forty holes in stainless while the other stops at one. The difference is in the steel, and it is not visible from the outside. Here is what each grade actually is.

The grades, plainly

Grade	What it is	Best for	Avoid for
HSS 4241	Low-alloy tool steel. Cheapest bright-finish bits.	Wood, plastics, occasional soft steel	Any production metalwork
HSS M2 / 6542	Proper high-speed steel — tungsten + molybdenum	Mild steel, aluminium, general trade use	Stainless, hardened steel
TiN-coated HSS	M2 with a titanium nitride surface layer, ~2,300 HV	Abrasive materials, cast iron, GRP, chipboard	Being resharpened (coating is surface only)
M35 cobalt (5% Co)	HSS with cobalt for red hardness	Stainless 304/316, tough alloys, heat-prone work	Impact use — slightly more brittle
M42 cobalt (8% Co)	More cobalt again, harder and hotter-running	Inconel, titanium, hardened alloys	General work — you are paying for nothing
Solid carbide	Tungsten carbide throughout, very hard, very brittle	CNC on rigid machines, hardened steel > 45 HRC	Hand drills — it will shatter

Drill bit grades and where each one earns its price

What "red hardness" means and why it decides everything

The property that separates these grades is not room-temperature hardness — it is how much hardness they keep when hot. A cutting edge in steel runs at several hundred degrees. Plain HSS starts softening around 550 °C. Add 5% cobalt and it holds its edge meaningfully hotter; that is M35.

This is why cobalt is the answer for stainless specifically. Stainless has poor thermal conductivity, so the heat generated at the cutting edge stays at the cutting edge instead of flowing away into the workpiece. The edge gets hot fast, and only a grade that stays hard when hot survives it.

From our range

Industrial 13-Piece M35 Cobalt Twist Drill Bit Set for Stainless Steel

M35 cobalt set, 135° split point — the practical choice for anyone regularly drilling 304 or 316.

Coated or uncoated?

Coatings are a surface treatment a few microns thick, so they change how the bit behaves at the surface without changing the steel underneath.

Bright / uncoated — the slickest surface, lowest friction. Best for aluminium and copper, where the enemy is material welding into the flutes.
Black oxide — a thin oxide layer that holds cutting oil and resists rust in storage. Cheap, mildly useful, mainly a corrosion and shelf-appearance benefit.
TiN (gold) — a genuinely hard ceramic layer, around 2,300 HV against roughly 900 HV for HSS. Extends life in abrasive materials. Worth it for cast iron, fibreglass and chipboard.
TiAlN (dark violet/black) — forms a protective aluminium-oxide skin at high temperature. Designed for high-speed dry machining, not for hand drills.

Rolled or fully ground — the difference nobody advertises

Independent of grade, there are two ways to make a twist drill:

Roll forged. Round stock is heated and the flutes are rolled in. Fast and cheap. The flute profile is approximate and concentricity is average, so holes come out slightly oversize and the bit is more likely to wander.
Fully ground. The flutes are ground from solid bar on a CNC grinder. Accurate flute geometry, concentric point, a genuinely sharp edge. Costs more to make and produces an on-size hole.

For wood and rough work, rolled bits are perfectly adequate and the price difference is real money at volume. For metalwork, fully ground is the one buyers come back for — the difference shows up within a dozen holes.

From our range

Industrial M2 HSS Fully Ground Twist Drill Bit (DIN 338) – OEM

Fully ground M2 to DIN 338 — the standard specification for metalworking distribution.

What to stock, if you are buying for resale

From what moves in the markets we ship to, a sensible core range is narrower than most catalogues suggest:

01HSS M2 fully ground, DIN 338, 1–13 mm — the volume line. Sells to every trade.
02M35 cobalt in the common sizes (3, 4, 5, 6, 8, 10 mm) — for the stainless fabricators. Higher margin, and the customer who needs it knows exactly why.
03TiN-coated sets — the retail-facing product. Gold bits sell on the shelf, and in abrasive material they genuinely last longer.
04A step drill or two — solves the sheet metal problem that twist drills handle badly, and it is an easy add-on sale.

Solid carbide and M42 are specialist lines. Unless you are supplying CNC shops directly, they tie up money on a shelf. Worth quoting when asked, rarely worth stocking deep.