Why the receiving board gets the small hole
A wood screw is a clamp: the head bears on the top board, the threads pull from the
bottom board, and the joint closes because the top board can’t grab the threads.
That’s the whole system — clearance hole up top, pilot hole below, countersink if
the head sits flush. Get those three diameters from the chart and screws stop
splitting rails, wandering off line, and snapping in white oak.
Gauge by gauge details, with the sizes repeated where a phone search can find them:
#2 · #3 · #4 · #5 · #6 · #7 · #8 · #9 · #10 · #12 · #14
Frequently asked questions
How do I pick a pilot hole size?
Match the pilot hole to the screw’s root — the solid core inside the threads. In hardwood, drill the root diameter so the threads cut wood without the core splitting it; in softwood, go one size smaller because the softer fibers compress. The chart above applies that rule for every common gauge.
What’s the difference between a pilot hole and a clearance hole?
The pilot hole (in the receiving piece) gives the threads something to bite without splitting. The clearance hole (in the piece being fastened) is slightly wider than the screw’s shank so the screw slides through freely and the head clamps the joint tight. Skip the clearance hole and the screw can hold the two boards apart instead of together.
When should I size the pilot hole up or down?
Size up 1/64″ in very hard or brittle stock (hard maple, hickory, white oak, most tropicals), near board ends, and for brass screws — brass twists off in a tight hole. Size down 1/64″ only in soft, stringy woods when a screw strips instead of seating.
Do these sizes work for modern production screws?
The chart is for traditional tapered wood screws and works for straight-shank production screws (deck, cabinet) too — their aggressive threads are more forgiving, and many are marketed “no pre-drill” in softwood. In hardwood, near an edge, or anywhere a split would hurt, pre-drill anyway. Pocket-hole and drywall screws use their own stepped bits and conventions.
What about countersinking?
The countersink column lists the bit that lets a flat head sit flush. A combination pilot-countersink bit sized to the gauge does pilot, clearance top, and countersink in one pass — worth owning in #6 and #8, the two gauges that drive most shop work.