Pilot hole

The pilot hole also reduces the power needed to turn a large drill bit, and reduces the large bit breakage risk.

For twist drill bits, the pilot size is usually selected so that the chisel point of the larger drill does not need to remove any material, which reduces the chance of splitting the web of the bit.

[1] On harder materials, such as most metals and many plastics, and sometimes on softer materials like wood, a center punch is used before drilling the pilot hole to ensure that the smaller pilot drill bit does not slip and that it starts at the correct location.

The appropriate pilot hole will prevent binding while providing sufficient friction to keep the screw from loosening.

For standard wood screws, special pilot drill bits are manufactured to produce the correct hole profile in a single operation, rather than needing several different drill bit sizes and depths.