Pilot hole and clearance hole, before you drive the screw
Two Fine Woodworking articles on why the top board and the bottom board are not the same hole. I have not driven the screw.
Researched in October 2026. Reviewed . Next review: April 2027. 3 sources
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Research guide: I have not tested these products. Affiliate disclosure As an Amazon Associate I earn from qualifying purchases.
How I built this guide
Sources I read. Mike Korsak, Fine Woodworking 288 (2021), and Robert J. Settich, Fine Woodworking 195 (2007).
What I cross-checked. That both size the clearance hole to the outside of the threads and the pilot to the root, and that Settich steps the pilot one bit for pine and for maple.
What I could not verify. A numbered drill chart. Neither article is a table I am copying, and screw diameters vary by batch.
Most sources suggest this if the top piece has to be pulled tight against the bottom piece; skip it if you want a pocket-hole screw, or a joint that is only glue.
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Dial caliper
Budget. More than one source agrees.
Korsak and Settich both measure the screw, instead of trusting a remembered chart. Korsak uses dial calipers on each batch.
I have not checked a current listing. The button is a search.
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Countersink bit
Budget. One source, no second opinion.
Korsak countersinks so the head can sit flush, and prefers a drill press so the countersink shares the hole’s center.
A comment on his article names a Lee Valley single-flute bit. I did not confirm the current page.
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A wood screw is two holes, not one. I have not drilled them. A pocket-hole screw is a different part, with its own jig, and that note is here.
What the two articles agree on
High on the idea. Two Fine Woodworking pieces, fourteen years apart, describe the same two diameters. Neither one is a lab I watched.
The clearance hole is in the top piece, the one the head has to pull down. Mike Korsak sizes it to the outside of the threads, or to the shank if the shank is bigger, and he wants the screw to slide in and out freely. If the hole is small, the threads bite the top piece as well as the bottom, and the head stops clamping.1 Robert J. Settich says the same thing in shop language: without that hole the pieces “jack,” meaning they do not draw tight. He sizes the clearance hole to the outside of the widest threads.2
The pilot hole is in the bottom piece, the one the threads have to hold. Both size it to the root, the metal between the threads. Korsak: too big and there is little wood left for the threads, so they strip; too small and the screw wedges, splits the wood, or breaks. Settich: with no pilot at all, the screw shoves fibers aside, which he says is tolerable in carpentry and a split waiting to happen in harder, thinner furniture parts.34
Settich adds a step Korsak’s public page does not: in very soft wood such as pine, one bit smaller than the root; in very hard wood such as maple, one bit larger. That is why the pine note points here. The species sheet is here.
What they add, and what I will not copy
Korsak measures one screw from each batch with dial calipers, because a remembered chart lies when the batch changes. He likes a drill press so the hole is vertical and a countersink shares the same center. Settich says overdriving, after the head is home, spins the threads and turns the wood to fluff, so the screw holds nothing. He would rather finish the last turns by hand, or set the clutch lower.56
I am not printing drill numbers. I did not measure a screw. A chart in a catalog is not this note.
My take
Top piece: a hole the screw can slide through. Bottom piece: a hole the threads can bite, sized from the screw in your hand, a bit smaller in pine and a bit larger in maple if you follow Settich. Then stop when the head seats. If the joint should not come apart and should not show a screw, the glue note is the other path, here.
The photo is a class bench of hand tools. It is not a set of bits.
Where this comes from
- Mike Korsak, Fine Woodworking. The subtleties of driving a screw. Magazine article, issue 288. Mike Korsak, Fine Woodworking Consulted 30 Oct 2026. back
- Robert J. Settich, Fine Woodworking. Use Screws Like a Pro. Magazine article, issue 195. Robert J. Settich, Fine Woodworking Consulted 30 Oct 2026. back
- Veta. When a pocket-hole jig is worth buying. This notebook. Veta 30 Oct 2026. back
Changes in this guide
- First note. Pocket-hole screws are a different fastener.
Common questions
Is one hole through both boards enough?
Not if you want the head to clamp. Korsak says an undersize hole in the top piece lets the threads bite there too, so the head stops acting as a clamp. Settich calls the gap that leaves “jacking.”
What diameter do I drill?
Measure the screw you are holding. Both writers size the clearance hole to the outside of the threads and the pilot to the root, between the threads. I am not printing a chart. Batches differ, which is why Korsak measures each batch.