Which Drill Bit for Metal? Start With the Metal and the Hole

For ordinary mild steel or aluminum, start with a sharp high-speed steel (HSS) twist drill bit. For repeated stainless-steel work, consider cobalt-alloyed HSS rated for stainless. For several hole sizes in thin sheet, consider a step bit. The metal, its condition and the hole depth matter more than the color of the bit.

Choose the bit for the workpiece

Your job	Sensible starting choice	What to check before buying
Small holes in mild-steel brackets or aluminum parts	HSS twist bit	Metal application rating, cutting diameter and usable depth
Holes in common annealed stainless steel	Sharp stainless-rated HSS; cobalt HSS is an upgrade to consider for repeated work	Stainless rating, point geometry and a stable setup
Several hole sizes in thin sheet metal	Metal-rated step bit	Material/thickness limit and whether it includes the exact diameter
Large opening in metal	Metal-rated hole saw or another application-specific cutter	Arbor fit, cutting depth and drill capacity
Heat-treated or hardened steel	Tooling selected for the actual hardness	Alloy, hardness and the tooling supplier’s application limits—not just “for metal” on the package

Norseman’s HSS drilling chart covers mild steel and aluminum, but directs users to consult the material supplier for high-tensile heat-treated material. A DEWALT drill manual identifies HSS twist bits and hole saws as metal-drilling options.

Stainless does not automatically require cobalt. The British Stainless Steel Association says standard HSS drills are suitable, while emphasizing sharp edges, rigidity and correct feed. Bosch offers cobalt-alloyed HSS bits specifically for stainless, describing their wear and heat resistance. Cobalt is a useful purchasing option, not a cure for a dull edge or a wandering drill. See the cobalt-bit selection guide for a closer comparison.

A step bit is a thickness-limited tool, not a replacement for a twist bit in thick plate. For example, Klein’s QRST01 covers 1/8–1/2-inch holes and is rated for steel up to 16 gauge. That limit belongs to that model; check the bit you intend to use.

Read the specification, not the finish

“Titanium” commonly describes a coating, whereas cobalt HSS describes an alloy. Norseman’s TiN-coated drill range includes both conventional HSS and cobalt HSS. The coating label therefore does not tell you the underlying steel or guarantee suitability for your workpiece.

Check three more details:

• Point: A split point can help the bit start accurately. Norseman describes its 135-degree split points as self-centering; a point angle alone is not the same thing as a split-point design.
• Length: Choose enough reach and drilling depth, without unnecessary length. BSSA recommends shorter drills for stainless to reduce deflection and breakage.
• Shank: Check the shank diameter against your chuck’s capacity. Cutting diameter and shank diameter may differ. For example, our 9/16-inch bit guide explains reduced-shank fit checks. A fitting shank does not establish drilling capacity: also check your drill manual’s metal-drilling limits.

For one repair, buy the required diameter rather than choosing a large set first. Establish whether the hole is for clearance or tapping before ordering; our 1/4-20 drill-size guide separates those tasks.

Set up the cut so the bit lasts

Clamp the work; do not hold a loose metal part by hand. Wear eye protection, keep hair and loose clothing away from rotation, and use the drill’s side handle if supplied. Select rotary drilling mode, not hammer mode. Support thin material with a backing block. These practices follow the DEWALT manual’s drilling and safety instructions.

There is no single “metal RPM.” As a calculated example, Norseman’s general HSS cutting-speed ranges give approximately:

1/4-inch HSS twist bit	Calculated RPM range
Mild steel, 0.2–0.3% carbon	1,220–1,680
Stainless steel	460–760

These use the manufacturer’s formula, RPM = 3.8197 × surface feet per minute ÷ diameter in inches. They are starting guidelines, not handheld test results. At the same cutting speed, a 1/2-inch bit needs half the RPM. Follow more specific bit-maker guidance when available. Source: Norseman feeds and speeds.

Apply straight, steady pressure sufficient to produce chips without bending the bit or stalling the drill. Use a suitable cutting lubricant for steel; the DEWALT manual lists brass and cast iron as dry-drilling exceptions and advises easing pressure as the bit breaks through. Keep chips evacuating rather than allowing them to clog the hole.

If stainless stops producing chips and the point only rubs, stop and reassess sharpness, speed and support. BSSA warns against dwelling or rubbing with work-hardening grades such as 304 and 316. Buying a more expensive bit without correcting that cut may repeat the failure. The stainless-drilling guide covers that diagnosis in more detail.