1/2 Tap Drill Size and Drill Bit for a 1/2

Use a 27/64 drill bit

1/2 · 0.4219 in / 10.72 mm · ~75% thread

A 1/2 inch tap is the 1/2-13 coarse UNC thread. A 27/64 inch bit is the correct tap drill for a strong thread.

At a glance

drillØ = major − (pitch × %thread) = 0.5 − (0.0769 × 0.75) = 0.4423 in → next standard drill 27/64 (0.4219 in / 10.72 mm)

The 1/2-20 fine thread (a 29/64 bit) is used where finer pitch is required. This covers 1/2-13 coarse.

A clearance hole lets the bolt pass through unthreaded – close fit keeps parts aligned, free fit allows movement.

Compare with adjacent threads – coarse, fine and the opposite measurement system:

The 1/2 diameter comes in both coarse and fine pitch. Each has its own tap drill: