Pilot Hole

A pilot hole is drilled slightly smaller than a screw's threaded diameter, giving the threads something to grip and cut into cleanly rather than forcing the screw to displace all that material itself -- which, especially near an edge or in dense or brittle wood, is a common way to split a board. Pair a pilot hole with a clearance hole in the piece above it, and often a countersink too, for a screwed joint that seats cleanly and pulls tight.