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Step Drill Bits

(10 products)

Step drill bits from Milwaukee and Irwin Unibit drill several diameters with a single bit. Models from 3/16 in to 1-3/8 in, numbered 1 to 10, to drill and enlarge holes in sheet and thin metal, in the shop or on the jobsite.
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Complete guide to choosing your step drill bits

How does a step drill bit work?

A step drill bit is shaped like a stepped cone. Each step matches a diameter. You drill a small hole, then push the bit to the step you want to enlarge it. A single bit replaces a series of bits.

It suits sheet and thin metal, where a standard bit can catch or distort the hole. Edges stay cleaner and deburring is reduced. It also drills plastic and thin aluminum.

Which number and diameter range to choose?

Sizes vary by diameter range. The Milwaukee number 3 covers 1/4 in to 3/4 in, the number 4 goes from 3/16 in to 7/8 in and the number 5 from 1/4 in to 1-3/8 in. The number 9 offers two steps, 7/8 in and 1-1/8 in.

Irwin Unibit bits are numbered 1 to 10. The number 4 is available in cobalt (10234CB) for harder steel. Choose the range that contains the diameters you drill most often.

Using and maintaining a step drill bit

Mark the center with a center punch and drill at moderate speed. Use cutting fluid, especially on steel. Apply steady pressure without forcing. Keep the drill straight to get a round hole.

Clear chips between steps. Clamp the sheet in a vise or with clamps so it does not spin. Clean the bit after use and store it dry.
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We answer your questions about step drill bits

What is a step drill bit used for?

A step drill bit drills and enlarges holes of several diameters with a single bit. It is ideal for sheet metal and thin metals. Each step matches a specific diameter, so you avoid changing bits.

What is the difference between a Milwaukee step bit and a Unibit?

Both work on the same principle, with steps of increasing diameters. Milwaukee offers sizes 3, 4, 5, 7 and 9, among others. Irwin offers Unibit bits, including the number 4 in cobalt. Choose based on the diameter range you need.

Can you drill steel with a step drill bit?

Yes, especially thin sheet metal. For harder steel, choose a cobalt model, such as the Irwin Unibit number 4. Use cutting fluid and moderate speed. See our cutting oils.

Which step drill bit should I choose to enlarge a 1/2 in hole?

Choose a bit whose range includes 1/2 in, such as the Milwaukee number 3, 4 or 5. The number 5 goes up to 1-3/8 in. Drill a small hole first, then enlarge it by pushing the bit to the step you need.

Does a step drill bit replace a drill bit set?

For thin sheet metal, often yes: one bit covers several diameters. For thick materials or very precise holes, a drill bit set remains more suitable. See our metal drill bits.

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