pilothole

A pilothole, more commonly written as pilot hole, is a small-diameter hole drilled into a material to guide a larger drill bit or to receive a fastener. The primary purpose is to improve drilling accuracy and reduce the risk of splits, wandering, or cracking, especially near edges or delicate features.

In woodworking, metalworking, and construction, pilot holes are used before screws, dowels, or bolts. For screws, the pilot hole size is chosen to balance ease of driving with sufficient thread engagement and to minimize splitting in wood or warping in softer materials. For metal operations, pilot holes may guide larger drill stages or prepare holes for tapping, reaming, or counterboring. In many cases, the hole is drilled with a smaller bit first, followed by a larger bit or a tap.

The technique involves locating the hole, often marking with a center punch, and drilling perpendicular to the surface. Material considerations determine the bit type (brad-point, twist, or Forstner bits for wood; twist or carbide bits for metal) and the drill speed. After drilling, the hole may be deburred, countersunk, or reamed for a precise fit.

Terminology varies by field; “pilot hole” is the standard term in most contexts, while some texts use the one-word variant pilothole. Regardless of spelling, the underlying concept remains a preliminary, guiding hole that facilitates accurate drilling and reliable fastener performance.