How to Choose a Drill Bit for the Hole You Need

Start with what the hole has to do, then pick the bit. First decide whether the screw should slide through the hole freely or bite into it. Then use the screw's size and the workpiece material to set the diameter, and finish by picking a bit material or tip shape that suits what you're drilling.

A wood-screw joint shows why the order matters. The top board and the board underneath need different holes. A bit that's right for the wood can still give you the wrong fit if you use it for both.

Choose the Hole Type Before the Bit Diameter

Good drill bit selection starts with the hole's purpose, because one screw can need two different holes. The Handyman's Daughter sizing guide names three factors for picking a bit size: your screw, hole type, and material. Work through them in this order:

1. Name the hole's job. In a wood-screw joint, a clearance hole in the top piece lets the screw pass through. A pilot hole in the receiving piece gives the threads something to grip. Settle which one you're drilling before you reach for a bit.
2. Identify the screw and the workpiece. Note the screw size from the package and whether the wood is softwood or hardwood. The same wood-screw guide shows pilot sizing by screw and wood type, so both details change the answer.
3. Look up the diameter for that exact combination. Ana White's pre-drilling guide suggests using the fastener manufacturer's pilot-hole chart when one is available. If your project plans call for a specific hole size, follow that.
4. Test before you drill the real part. The same guide recommends that you test the bit and screw in an offcut from the same board. If you're working with our K2 Ultra, the K2 Ultra drill setup guide walks through installing a bit and drilling with control.
5. Choose the bit material and tip shape. Once the diameter is set, match the bit to the workpiece using the examples in the material section below.

The offcut test shows you how the screw behaves in that board at that diameter. If the screw doesn't pass through or grip the way the joint needs, switch bit sizes and test again on scrap. Don't move to the finished piece until the test looks right. This order also explains why picking a bit by material alone falls short. Material tells you what kind of bit can cut the workpiece. It doesn't tell you how big the hole should be for the fastener.

No single diameter works for every screw. The right number comes from the fastener's chart or your project plans, applied to the hole type you named in step one.

How Clearance and Pilot Holes Differ in a Wood-Screw Joint

The two holes sit in different boards and do different jobs, so one bit isn't automatically right for both. The DIYdata wood-screw guide spells out the clearance and pilot hole roles like this:

• Clearance hole: It goes through the top piece. Its job is to let the screw pull that piece tight against the surface underneath. The threads shouldn't grab the top board, so this hole is sized for the screw to pass through.
• Pilot hole: It goes into the receiving piece, the board the screw actually holds. This is where the threads need to bite.
• What sets the pilot size: The guide's chart lists pilot holes by screw size and wood type, with separate columns for softwood and hardwood. One screw can need one pilot bit in pine and a different one in oak.

In practice, a single screw joint can call for two bit sizes. One drill pass through both boards with the same bit skips the step that lets the top piece seat firmly.

That chart lists screws by gauge on an Imperial scale, and it's one guide's reference rather than a U.S. standard. Match your screw to the size printed on its package. When the screw maker publishes its own pilot-hole chart, use those numbers for that fastener.

Match the Bit's Material and Geometry to the Workpiece

Once the diameter is set, pick a bit material that suits the workpiece and a tip shape that suits how exactly the hole has to land. The table covers the wood and metal examples supported by the guides cited here.

Bit material and tip shape answer two different questions. HSS and cobalt describe what the bit is made of, which is about whether it can cut the workpiece. A brad-point bit is about where the hole ends up, so it matters most when a pilot hole has to line up with a mark on furniture or trim.

For metal, the choice depends on the alloy. The HSS and cobalt uses come from the selection guide of industrial supplier Fastenal. Its cobalt list is limited to the tough metals it names. If your part isn't one of those metals, the HSS listing for metal is the closer match. If it is one of them, use cobalt.

These examples cover wood and metal only. For masonry, concrete, tile, or plastic, go by the material rating on the bit maker's packaging, and still use the hole-type steps above to set the diameter.

FAQs

Do I always need a pilot hole for a wood screw?

Not always. The DIYdata guide says that when the underlying wood is softwood and the screw is smaller than gauge 6, a drilled pilot hole usually isn't needed. Larger screws, and screws going into hardwood, fall outside that exception, so look up the pilot size for those.

Can I use a brad-point bit on metal?

The guide that recommends brad-point bits discusses them for woodworking jobs where accurate placement matters. For metal, use the bit materials Fastenal lists for metal work: high-speed steel in general, and cobalt for the tough metals it names.

Does the clearance-and-pilot approach apply to masonry or tile?

The idea of naming the hole's job first still applies, since the hole type and material are both part of sizing any bit. The wood-screw chart and the bit examples here don't cover masonry or tile, though. Take the diameter from your anchor or fastener maker's instructions, and pick a bit rated for that material.

Why might the same screw need a different pilot bit in a different board?

The pilot chart in the DIYdata guide has separate softwood and hardwood columns for each screw size. If you move a screw from a softwood shelf to a hardwood frame, check the hardwood column and test on scrap from the new board before you drill.