Choose Metal Drill Bits That Match Your Actual Job

The best drill bits for metal depend on the job: choose the DeWalt DWA1184 HSS set for ordinary mild-steel repairs, Bosch M42 cobalt bits for repeated stainless-steel drilling, Norseman Type 190-SS high-helix bits for recurring aluminum work, or the Irwin Unibit 10231 for several hole sizes in thin sheet. None is a universal replacement for the others.

These are application-based recommendations from manufacturer specifications, not a hands-on ranking. We have not measured comparative drilling speed, hole accuracy or bit life, and the available research provides no price comparison. For a mixed-material kit, see our broader best drill bits guide.

Select your metal-drilling job to see the recommended bit and its main limitation.

Mild-Steel Repairs: DeWalt DWA1184 HSS Set

Choose this set for occasional metal drilling when you also need bits for wood and plastic.

DeWalt specifies high-speed steel construction, a 135° split point intended to reduce walking, and three-flat shanks intended to reduce slipping in the chuck. The DWA1184 contains 14 bits spanning 1/16 to 1/2 inch, including two 1/8-inch bits. DeWalt lists it as a standard, rather than impact, accessory. DeWalt’s specifications and contents

It is a sensible starting point for mild-steel brackets and mixed household repairs. Its limitation is coverage: 14 pieces means 13 distinct diameters, not every fractional size between the endpoints. It omits sizes such as 11/64 and 7/16 inch. Check your required hole diameter before buying.

The finish is not a reason to treat this as a specialist stainless-steel set. DeWalt describes its Black & Gold coating in terms of rust and wear prevention; its material rating is broadly “metal.” Buy it for its useful assortment and general-purpose construction, not an assumption that the coating makes it suitable for every steel.

Repeated Stainless-Steel Work: Bosch M42 Cobalt Bits

Choose these when stainless steel is a regular job, especially if you only need a few diameters.

Bosch’s M42 jobber-length bits contain 8% cobalt and are explicitly intended for stainless steel, cast iron, titanium, light-gauge metal and aluminum. Individual sizes run from 1/16 to 1/2 inch, with working lengths listed separately from overall lengths. Bosch specifies rotary drill/driver use and compatibility with three-jaw chucks. Bosch M42 specifications

Buying individual bits makes sense for repeated holes in one size: you can buy the exact diameter and a spare rather than another case of mostly unused bits. If you need a set, Bosch’s CO14B contains 14 pieces from 1/16 to 1/2 inch, again with a duplicate 1/8-inch bit rather than a complete fractional sequence. Bosch cobalt-set contents

Do not interpret “cobalt” as permission to run fast or drill every hardened part. The exact application and setup still matter. Our cobalt drill-bit guide covers the selection checks in more detail.

Recurring Aluminum Work: Norseman Type 190-SS Bits

Choose these for aluminum work where chip evacuation matters.

Norseman recommends its Type 190-SS high-helix design for aluminum and other nonferrous metals, as well as stainless steel. It describes the flutes as particularly useful for lifting chips from aluminum and other soft materials. The bits have a 135° split point; the 41601 set covers 1/16 to 1/2 inch in 1/32-inch increments. Norseman’s high-helix range

This is a geometry-led choice, not a claim that every aluminum hole requires a specialist bit. For one occasional hole, a suitable general-purpose twist bit may be enough. For repeated work, flute design and chip clearance deserve more attention than a gold-colored finish.

Unlike the two 14-piece assortments above, the stated 1/32-inch sequence tells you the spacing between included diameters. It still does not establish that the set contains a particular metric, number or letter size required by your job.

Thin Sheet Metal: Irwin Unibit 10231

Choose this step bit for several hole diameters in thin panels, not deep holes in plate.

The Unibit 10231 is an HSS step bit covering 1/8 to 1/2 inch in 1/32-inch diameter increments. Irwin specifies a single-flute cutting edge, marked sizes and a hex shank, and recommends it for thin materials including stainless steel, copper, brass and aluminum. Irwin’s product specifications

Grainger lists this model as not impact-rated and describes its use in material up to 1/8 inch thick. That stated thickness limit is more important than the largest diameter printed on the bit. A hex shank alone does not establish impact compatibility. Unibit 10231 fit and thickness details

For thin stainless sheet needing several diameters, this is a different application from repeated constant-diameter holes with a cobalt twist bit. Select by hole shape and stock thickness as well as the metal’s name.

A step bit does not replace a twist bit for a deep, constant-diameter hole. See our guide to what a step drill bit is used for before buying one for thicker stock.

Exact Diameter and Working Length Can Rule Out a Set

Buy for the finished hole, not the set’s piece count. A fractional assortment may not contain the number, letter or metric drill required by a tap. The DeWalt and Bosch assortments illustrate the problem: their endpoint sizes do not mean every size between those endpoints is included.

Confirm chuck capacity, shank compatibility and usable cutting length before ordering. A bit’s overall length is not its drilling depth. Bosch lists working and overall lengths separately, so use the working-length specification when checking whether a particular bit can reach through the stock.

Keep the tool rating separate from the shank shape. DeWalt lists the DWA1184 as a standard accessory, Bosch specifies rotary drill/driver use for its M42 range, and Grainger identifies the Unibit 10231 as not impact-rated. None of those specifications establishes suitability for an impact driver.

Hardened Steel Needs a Separate Selection

Do not assume a cobalt set covers a hardened shaft, die or bearing component. Match a carbide drill’s stated application to both the material and machine; Dormer notes that some high-performance carbide drills fail when a setup lacks the necessary runout accuracy and feed control. Dormer’s carbide application distinctions

That is a reason to check the setup, not simply buy the hardest bit available. Use our hardened-steel carbide drill guide for this case. The four picks above do not establish a recommendation for an unspecified hardened part.

Match RPM to the Metal and Bit Diameter

There is no single “metal RPM.” Norseman’s general HSS guidance gives stainless steel 30–50 surface feet per minute and mild steel 80–110. Its formula is RPM = 3.8197 × surface feet per minute ÷ bit diameter in inches. Norseman’s speed table and formula

A 1/4-inch HSS bit in stainless therefore works out to approximately 460–760 RPM. That is a calculated starting range, not a tested setting for every stainless grade or the Bosch range. Larger diameters require lower RPM at the same surface speed; the setting that works for a small bit should not automatically carry over to a larger one.

Clamp the work, wear eye protection and keep the bit cutting with controlled pressure. Use a cutting lubricant suited to the metal and tool instructions; DeWalt’s drilling guidance identifies cast iron and brass as dry-drilling exceptions. DeWalt drilling instructions

Ease pressure as the bit breaks through. Stop the machine before brushing away chips, and never hold drill-press work by hand or wear gloves while operating it. CCOHS drill-press safety guidance