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A pilot hole is a smaller hole drilled into a material prior to a larger hole being drilled, widening the hole to the desired width. Drilling a pilot hole prevents a larger drill bit from slipping on the material - a potential safety hazard, as well as an increased likelihood of the work being damaged. Normally, a center punch is used before drilling the pilot hole to ensure that the smaller pilot drill bit does not slip.

Pilot holes may also be used when driving a screw. When a screw is driven into a material, it can act as a wedge, generating outward pressure which can cause many materials (such as wood or plastic) to split. By drilling a small pilot hole into the material, into which a screw is then driven, less 'wedging' takes place, thereby reducing the likelihood of the material being split.

Pilot holes are used on a variety of materials including wood and plastics, though their use is especially essential when drilling into polished or smooth metal, as larger drill bits are very likely to slip on such materials.

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• The influence of pilot hole diameter on screw pullout resistance
• Recommended Pilot Hole Sizes in Metal, Inch and Metric
• Recommended Pilot Hole Sizes in Wood