Step Drill Bit for Stainless Steel: Hex Impact or 3/8 Shank

A step bit is a cone of drill sizes stacked on one shank. You push, it cuts a step, you keep pushing, it cuts the next one. You stop when the hole is the size you want. Stainless is where the wrong pick shows fastest: a bit that cuts mild steel all day can burn out in one hole. Slide the ruler below to your hole and it shows every bit we carry that cuts it, with the speed to run it.

What is the best step drill bit for stainless steel?

The best step drill bit for stainless steel is M35 cobalt with a TiAlN coating, run slow with cutting oil. Cobalt holds its edge at the heat stainless makes. ITM rates its plain M2 bits for "sink grade" stainless only, meaning thin sheet. For panels, enclosures and anything thicker, use the XSTP-01 (1/8 to 1/2 in., $37.96), XSTP-03 (1/4 to 3/4 in., $45.95) or XSTP-04 (3/16 to 7/8 in., $59.09). Each costs about 16% more than the matching M2 bit.

Speed matters more than the bit does. Set the drill for the biggest step you'll cut and leave it there. In stainless that's about 300 RPM for a 1/2 in. step, 200 for 3/4 in. and 170 for 7/8 in. If you ask an AI chatbot, you may hear 250 to 350 RPM for 7/8 in. That's twice our number, and it burns the edge. The full table for aluminum, mild steel and stainless is in our drill speed chart.

• Push hard and keep cutting. If the bit spins without cutting, stainless work-hardens, and the next step will just rub.

• Flood it with oil. Add more for every hole.

• Use a drill, not an impact. You can't hold an impact at 170 RPM.

• Blue chips or a squeal mean it's too hot. Slow down and push harder.

Which step drill bit fits an impact driver?

Only a 1/4 in. hex shank step drill bit fits an impact driver. It snaps into the driver's quick-release collet the same way a screwdriver bit does, and it also fits any three-jaw drill chuck. The 3/8 in. shank needs a drill chuck: a cordless drill-driver, a corded drill or a drill press.

ITM builds both from M2 high-speed steel at nearly the same price. The difference is what else comes with each shank:

Verdict: go hex if your impact driver is the tool already in your hand, and go 3/8 in. for 1 in. conduit knockouts. On the same range, the shank costs you $2 or less, so let the size and the metal decide.

One caution: an impact driver hammers once it meets resistance, and you can't hold most of them at a slow, steady speed. That's fine in thin mild steel and aluminum. In stainless, put the same hex bit in a drill-driver set to low gear. The impact vs regular bit tips guide explains what "impact rated" means on a shank.

What size step drill bit do I need?

You need the step drill bit whose top step is at least as big as your biggest hole, and that also has your smaller sizes on the way up. For conduit, the hole is bigger than the trade size, because the connector's threads have to pass through:

Knockout sizes follow standard trade-size knockouts. Bolt clearances are normal fit per ASME B18.2.8.

If 7/8 in. is the only size you drill, the single-step 7/8 in. smooth cone step drill (274MC0010) does that one hole without the ridges a stepped bit leaves. For holes over 1-3/8 in., switch to a hole saw. The table at the end of this guide lists those.

Two ways to stop on the right step: count the steps as they cut through, or slide a washer over the bit to act as a stop. ITM suggests both. A marker line on the step below your size works too.

How thick a metal can a step drill bit cut?

A step drill bit cuts sheet up to about 1/8 in. thick. Each step is only that tall. If the sheet is thicker, the next step starts widening the top of the hole before the current one has broken through the bottom. ITM rates its step drills for sheet "up to 1/8 in. thick", and the 274MC0011 has 3/16 in. deep steps for a little extra room.

Plate, flange and angle need a different tool. Use a Silver and Deming bit for 33/64 to 1-1/2 in. bolt holes in plate, or a bi-metal hole saw for big holes. For hard or abrasive steel, see drill bits for hardened steel.

Step drill bit or hole saw: which is cheaper?

A hole saw is cheaper if you only ever cut one size, and a step bit is cheaper once you need three or more sizes. Our 7/8 in. bi-metal hole saw (275HW0016) costs $7.94 each with a minimum order of 4. Our 13-step 1/8 to 1/2 in. hex bit (274HEX01) costs $32.86 for 13 sizes, about $2.53 a size. A step bit also leaves a cleaner edge in thin sheet and doesn't grab and twist your wrist at breakthrough. Use a hole saw past 1-3/8 in. and in sheet thicker than 1/8 in.

Which step drill bits does Eldorado Tools carry?

We carry 20 ITM step drills that cover 28 hole sizes from 1/8 to 1-3/8 in., in three lines. The M2 1/4 in. hex impact line has 6 bits. The M35 cobalt TiAlN 1/4 in. hex line has 3. The M2 3/8 in. shank line has 11. All of them are sold each, and four have a minimum order of 2. Shop them all in step drills, or go straight to impact-ready hex shank or standard shank.

Prices are each, from our catalog on Oct 29, 2026. "Backordered" means open orders are waiting on ITM. We don't promise a ship date.

Tap every hole size you drill in a normal week, or start from your trade, and the kit builder picks the fewest bits that cover them.

What else goes in the bag with a step bit?

A step bit leaves a clean edge in thin sheet, but it isn't the whole job. Here's what usually rides along with it:

• Bigger knockouts: use the bi-metal hole saws above, with an arbor from arbors and adapters.

• Burrs on the back side: a 60° deburring tool, 7/16 to 25/32 in. (DC-26) at $34.07 cleans conduit holes. For screw heads, see counterbore vs countersink.

• Tek screws on duct and strut: a 5/16 in. magnetic impact nut setter (IMP-042-20) at $3.00 goes in the same impact driver as your hex step bit.

• Sockets on that impact: impact socket adapters.

• Cutting the stainless strut or conduit first: stainless-safe cut-off wheels.

• Twist bits for metal: how to choose drill bits for metal.

Not sure which bit fits the box, panel or sink in front of you? Call our team at (833) 4-ETOOLS or email sales@eldoradotools.com with the hole size and the metal.

Sources: ITM step drill product specifications (step lists, shanks, sheet thickness rating, sink-grade stainless rating); Eldorado Tools drill speed chart (cutting speeds of 250, 90 and 40 SFM for aluminum, mild steel and stainless); ASME B18.2.8 normal-fit clearance holes; standard knockout sizes for conduit trade sizes.

First published [date], with prices checked in our catalog on Oct 29, 2026.