Reference guide
Pilot Hole vs Clearance Hole
The difference between pilot holes, tap drill holes, and clearance holes with practical examples.
A pilot hole guides a screw
A pilot hole is smaller than the screw threads. It helps the screw start straight and reduces splitting or screw breakage. Pilot holes are most common in wood, plastic, and other materials where a screw forms its own path.
A clearance hole lets the fastener pass through
A clearance hole is larger than the screw or bolt shank. It lets the fastener pass through the top part so the threads can pull the lower part tight. Close-fit clearance helps alignment. Free-fit clearance makes assembly easier.
A tap drill hole is different again
A tap drill hole is sized so a tap can cut or form internal threads. It is not meant to let the screw pass freely, and it is not the same decision as a wood screw pilot hole.
Related references
Drill Size ChartFind fractional, number, letter, and metric drill sizes with decimal inch and millimeter equivalents.Tap Drill ChartLook up recommended tap drill sizes for UNC, UNF, and metric threads.Clearance Hole ChartCompare close-fit and free-fit clearance holes for common screws and bolts.Printable Drill Tap ChartPrint compact drill, tap, clearance, and pilot-hole sheets for shop use.