Fastener Hole Reference

Pilot hole

A pilot hole guides a screw and reduces splitting or excessive driving force. The correct size depends on the screw root diameter, material, and whether full thread engagement is needed.

Tap drill

A tap drill leaves material for internal threads. The drill is smaller than the finished major thread diameter. Thread percentage and material affect the preferred size.

Clearance hole

A clearance hole lets the fastener pass through without threading into that part. Close, normal, and loose clearances serve different assembly needs.

Counterbore and countersink

A counterbore has a flat bottom for a cylindrical head. A countersink is angled for a flat head. Match the feature to the actual fastener instead of assuming the head angle or diameter.

Use the chart as a starting point

Reference values help compare sizes and plan a job. Product specifications, codes, tolerances, and the actual material still control the final choice.