About this site

What Size Drill Bit is a reference for the drill size you need: tap drill sizes for inch, metric and pipe threads, and pilot holes for wood screws and lag screws. Each size has its own page, and there are printable charts for the shop wall.

Where the sizes come from

Tap drill sizes are calculated from the thread geometry for about 75% thread, then compared against published machinist charts. Where charts disagree we say so on the page. Pilot hole sizes for wood come from published wood-screw and lag-screw charts. Lag screw pages show a range because those charts do not match.

Use the sizes with judgment

Material, tap type and machine rigidity all change what works best. If your tap or screw maker lists a different drill, use theirs. Test in scrap when it matters.

Found a mistake?

Email [email protected] with the page and the value you think is correct. We check every report.

The site is published by Evergreen Digital Media LLC.