How to Choose Drill Bits for Metal (and Make Them Last)

What drill bit should I use for metal?

A drill bit for metal is a twist drill made of high-speed steel, cobalt or carbide, with a cone-shaped point of 118° or 135°. You choose one by four things: what the bit is made of, its finish, its point angle and its length. This table gives our pick for each common metal, priced at the 1/4 in. size.

Store prices on Sept 27, 2026. Our drill bits are priced per bit and sold by the sleeve, usually 6 or 12.

If you only buy one kind, buy a 135° split-point, heavy-duty HSS jobber bit. It drills mild steel, iron, aluminum, wood and PVC, in a hand drill or a drill press. Browse every size in our high-speed drill bit collection.

What is the best drill bit for stainless steel?

The best drill bit for stainless steel is a cobalt bit with a 135° split point. Cobalt bits are HSS with 5–8% cobalt mixed through the whole alloy (grades M35 and M42). The cobalt keeps the cutting edge hard at the high heat stainless makes. Plain HSS softens and dulls in a few holes.

Technique matters as much as the bit in stainless steel. Stainless work-hardens: if the bit rubs instead of cutting, the surface under the tip gets harder than the bit.

• Run slow. About 600 RPM for a 1/4 in. bit, and about 300 RPM for 1/2 in.

• Push hard and steady. The bit should make a curl of chip, not dust. Never let it spin in place.

• Use cutting oil. A few drops on every hole cut heat and add life.

• Do not stop and restart in the same hole. Each restart rubs a hard layer in the bottom of the hole.

Cobalt, titanium or black oxide: which drill bit is worth it?

A cobalt drill bit is worth the extra cost in stainless and hard alloys. A titanium (TiN) bit is worth it for heavy use in mild steel and cast iron. Black oxide and black and gold bits are the best value for everyday steel. All four start as high-speed steel. What differs is the alloy and the coating.

Do the math by the hole, not by the bit. A cobalt bit costs about 2.4 times as much as a black and gold ThunderBit ($7.80 vs $3.24). In stainless steel, where plain HSS may stop cutting after a few holes, cobalt easily makes that up. In mild steel, the cheaper bit usually wins.

A titanium coating is only on the surface. Once you resharpen a TiN bit, the new cutting edge is plain HSS. A cobalt bit is the same metal all the way through, so it keeps its edge after sharpening.

Triumph rates its ThunderBits to drill up to 8 times as many holes as a standard general-purpose bit. The tapered web gets thicker toward the shank, which is why they snap less in a hand drill.

What length drill bit do I need?

Use the shortest drill bit that leaves about two bit diameters of flute outside the hole. The flutes are the spiral grooves. They carry chips and heat up and out. If the flutes are buried in the hole, chips pack in, heat builds and the bit dies early.

"Leave about twice the bit's diameter of flute sticking out of the hole. That gives the chips, the dust and the heat a way out. Bury the flutes and all of it gets trapped, and the bit dies a lot sooner."

David Castro, President, Eldorado Tools

So the deepest hole a bit should drill is its flute length minus two diameters. This table applies that rule to our own flute lengths.

Flute lengths from our Triumph HD stubby (T4HD), HD jobber (T1D) and 118° aircraft extension (T1290) bits.

Example: a 2 in. deep hole with a 1/4 in. bit needs a jobber, because a stubby tops out at 7/8 in. A 1/2 in. deep hole in 1/4 in. plate is a stubby job. The shorter bit is stiffer, so it walks less and snaps less.

• Stubby (screw machine) length: the stiffest bit. Best for sheet metal, thin plate, tight spaces and CNC work. See stubby drill bits, such as the 060416 at $3.00 each.

• Jobber length: the standard length in most sets. Right for most holes in a drill press or hand drill.

• 6 in. and 12 in. HD extension bits: a jobber-length flute on a longer shank. They add reach past a flange or through a frame, not hole depth. See the 057516 (6 in., $5.90 each) and 058516 (12 in., $10.75 each).

• Long-flute aircraft extension bits: a 9 in. flute on a 12 in. bit, or 13 in. on 18 in. These drill deep holes. See the 059816 (1/4 x 12 in., $31.68) and extra-length bits.

Should I use a 118° or 135° drill bit point?

Use a 135° split point for steel, stainless and most metal work, and a 118° point for aluminum, brass, wood and plastic. The 135° point is flatter and stronger. The split point adds small cutting edges at the center, so the bit starts where you put it without a center punch or pilot hole.

A 118° point is sharper, so it bites faster in soft metal. It walks more on hard or curved steel. That is why most heavy-duty bits, including all of our ThunderBits, use a 135° split point.

What speed should I drill metal at?

Drill metal slower than wood, and slower still as the bit gets bigger. A good starting speed is RPM = 3.82 × cutting speed ÷ bit diameter. The table uses common starting cutting speeds for HSS bits (cobalt for stainless).

Starting cutting speeds used: aluminum 250, brass 150, mild steel 90, cast iron 70 and stainless 40 surface feet per minute.

Most cordless drills run about 400–600 RPM in low gear and 1,500–2,000 RPM in high. Use low gear for stainless steel and for any bit over 3/8 in. If the chips turn blue or the bit squeals, slow down. Our guide to proper RPM and overheating explains why heat is what kills drill bits.

Will these drill bits fit my drill?

Yes. A round-shank jobber bit up to 1/2 in. fits any 3/8 in. or 1/2 in. drill chuck, including DeWalt, Milwaukee, Makita, Ryobi and Bosch drills and drill presses. For other drivers, pick the shank to match.

• Round shank: standard. Fits any 3-jaw chuck.

• 3-flat shank: three flats on the shank so the chuck jaws cannot slip. Good for high-torque cordless drills. See the ThunderBit+ 3-flat (12-pack, $41.57, about $3.46 per bit).

• 1/4 in. hex shank: snaps into an impact driver or quick-change chuck. See the 255HEX1664.

• 1/2 in. reduced shank (Silver and Deming): drills 9/16 in. to 1-1/4 in. holes with a 1/2 in. chuck. See Silver and Deming bits.

Need a size that is not a fraction, such as a #29 or letter F? Our drill size and tap drill chart lists every number, letter and metric size with its decimal.

How do I make drill bits last longer in metal?

Most drill bits for metal die from heat, not wear. Keep the speed down, keep steady pressure on the bit, use cutting oil, and clear chips from deep holes.

• Let the bit cut. Firm pressure makes chips. Light pressure makes the bit rub, heat and dull.

• Use cutting oil on steel and stainless. Aluminum can use oil or a little WD-40. Cast iron and brass drill dry.

• Peck deep holes. Back the bit out every half inch or so to clear chips.

• Clamp the work. A spinning part can cut you and snaps bits.

• Drill a pilot for big holes. Over 1/2 in., a 1/8 in. or 3/16 in. pilot makes the big bit cut easier.

• Ease off at breakthrough. The bit grabs as it exits thin metal. Back off pressure near the end.

Troubleshooting

For the bigger picture of drill bit types, from wood to masonry, see Drill Bits 101. Questions about a job? Call our team at (833) 4-ETOOLS or email sales@eldoradotools.com.

Published Sept 27, 2026. Prices checked on the store that day.