Drill bit for screw size.
The right pilot, tap, or clearance hole for any screw — adjusted for material. Softwood, hardwood, metal, and plastic all need different sizes.
How this works
Three different "drill for screw" questions get conflated in real life:
- Pilot hole — a hole that a self-tapping screw screws into. Sized smaller than the screw so the threads bite, but big enough that the wood doesn't split. Used for wood screws and sheet-metal screws.
- Tap drill — a hole that gets cut to threads with a tap. Sized to leave ~75% of the thread height when the tap cuts. Used for machine screws into solid material.
- Clearance hole — a hole the screw passes through freely. Sized slightly larger than the screw OD. Used in the top piece of a two-piece joint (the bottom piece gets the pilot or tap drill).
Material matters too. Softwood compresses; hardwood splits. A pilot hole that's perfect in pine will crack walnut. This calculator picks the right size given both pieces of information.
Sources
- Wood screw pilot holes: American Wood Council guidance; cross-checked with screw manufacturer (e.g., GRK, Spax) recommendations.
- Tap drills: Machinery's Handbook 31st ed., Table 3 — Tap Drill Sizes for 75% Thread.
- Clearance holes: ASME B18.2.8 — Clearance Holes for Bolts, Screws, and Studs.
Disclaimer. Recommended bit sizes are starting points. Wood density varies by species, grain orientation, and moisture content — what works in dry softwood may split when used on dense hardwood near a board edge. For critical or visible joints, test on scrap first. For threaded holes in metal, follow your tap manufacturer's specific drill recommendation when given.