Hole Saws and Step Bits for Ductwork and Sheet Metal (2026)
Duct and panel holes are thin metal. You want a round hole, a clean edge, and a cutter that does not grab the sheet. Two tools cover it: a hole saw for larger rounds (takeoffs, access, pipe passes) and a step bit for the smaller penetrations in panels and duct wall.
This is a buying split, not a test report. Listings change. Match the diameter and the shank to the hole you need, on the current manufacturer page. SDS-plus, SDS-Max, and concrete core bits are the wrong family. Leave them on the hammer drill.
Hole saw or step bit
| Hole | Tool | Why |
|---|---|---|
| About 1/4 in to 1-3/8 in in thin sheet or a panel | Step bit (uni-bit) | One bit, several diameters, less grab than a twist bit in sheet |
| Larger round opening in duct or a cabinet | Bi-metal hole saw and arbor | The cup cuts the diameter you need for a collar, boot, or access ring |
| Stainless duct or thick stainless panel | Carbide-tooth hole saw, slow, with oil | Bi-metal dulls fast in stainless |
| Concrete, block, or a hammer drill | Not these tools | Core bits and SDS masonry bits are a different job |
Galvanized duct is thin. A hole saw still needs a pilot so the cup does not walk, and you still deburr. A step bit is the better default under about 1-3/8 in because the steps limit how deep the bit dives and one shank covers the knockouts techs actually drill.
Hole-saw kits for duct and access holes
Buy a bi-metal kit whose diameters match the collars and access holes you cut, plus the arbor. Typical service kits land in the 3/4 in to 2-1/2 in range. Larger boots need the specific cup, not “the rest of the kit.”
Check three things on the listing:
- Arbor included or not. Cups alone do not run.
- Thread. Small cups are usually 3/8”-24. Larger cups are usually 1/2”-20. The arbor has to match.
- Pilot bit. Replace it when it dulls. A dull pilot is why the saw walks in sheet metal.
Use a rotary drill with a side handle. An impact driver smacks the teeth and ovalizes the hole. Low speed. Do not lean through the far side of the duct and into a liner, wire, or coil you did not look at.
For stainless, switch to a carbide-tooth cup. A general bi-metal kit is for galvanized, aluminum, and mild sheet.
Step bits for panels and duct holes
A step bit is for sheet, not for plate. Makers rate them for thin stock (often up to about 1/8 in, sometimes less — read that line). Split-point or self-starting tips matter because a walking bit in a panel door ruins the face.
- Double-flute bits tend to pull chips and leave a rounder hole in thin metal.
- Titanium or cobalt coatings are wear claims from the maker. They are not a license to drill stainless plate.
- Shank: 1/4 in, 3/8 in, or hex. Match the drill you already carry. A hex shank that fits your impact is still a bad reason to run a step bit on impact mode. Use drill mode.
One 1/8–1/2 and one 1/4–1-3/8 cover most panel penetrations and small duct holes. Add a hole saw only when the hole is larger than the biggest step.
Deburr both sides. A sharp lip cuts flex and hands, and it keeps a gasket from sitting flat.
What not to buy for this work
- SDS-plus or SDS-Max bits. Wrong chuck, wrong job.
- Concrete core bits. They are for masonry, not duct.
- A wood spade bit or a dull twist bit in galvanized sheet. They grab and throw the duct.
Before you order
Confirm diameter, shank, included arbor, and the maker’s max thickness. Prices on Amazon move. If the title says “hole saw” and the photo is a masonry core, skip it.