Pilot Holes in Wood: Why They Matter and How to Choose One
A pilot hole is a smaller hole drilled before driving a screw. It can reduce splitting, make driving easier and improve the repeatability of a joint. In harder or brittle wood, that preparation can be especially helpful.
Pilot hole vs. clearance hole
A pilot hole primarily guides the threaded portion of the screw. A clearance hole is sized so the screw's shank can pass through the top piece without its threads biting that piece. Many joints can use both: a clearance hole in the first board and a pilot hole in the second.
Hardwood vs. softwood
Denser wood generally benefits from a larger starting pilot than softer wood for the same screw, because the threads need more room to cut into the material without excessive driving force. That does not mean every hardwood uses the same size.
Avoid over-drilling
A hole that is too large can reduce thread engagement and holding power. A hole that is too small can make the screw difficult to drive and increase the risk of splitting or snapping. Make a test hole in a scrap of the same material whenever the fit matters.
Start with the MakeGauge finder
Use the Drill Bit / Screw Finder as a starting point, then test on scrap and follow the screw manufacturer's guidance for critical or specialty applications.