Tap drill answer
What Size Drill Bit for 1/2-13 UNC Tap?
For a 1/2-13 UNC tap, a common reference drill is 27/64, which is 0.4219 in or 10.72 mm. Verify the value for material, tap type, and required thread engagement.
1/2-13 UNC tap drill quick answer
Method: Named UNC and UNF drill sizes are maintained as common cutting-tap reference values and checked against manufacturer ranges. Reviewed 2026-07-24.
How to use this 1/2-13 UNC value
This page gives a common chart value for hand tapping and general reference work. Use a different value when your drawing specifies a thread class, percent thread, forming tap, pipe thread, thin wall, brittle material, or plated/coated part.
- Start with the listed drill size.
- Confirm the tap type and thread engagement target.
- Test in scrap material when fit matters.
- Use cutting fluid and proper chip clearing for deeper holes.
What drill bit size is used for a 1/2-13 tap?
A common chart value for a 1/2-13 UNC tap is 27/64 in, which is 0.4219 in or about 10.72 mm. This answer applies to the 13 TPI coarse thread.
Is 27/64 the standard 1/2-13 tap drill?
27/64 in is a common cutting-tap reference. Verify the tap maker's recommendation when material, hole depth, thread class, or forming-tap use changes the required engagement.
What is the 1/2-13 tap drill size in millimeters?
27/64 in converts to about 10.72 mm. If an inch drill is unavailable, compare the actual metric diameter and expected thread engagement before substituting.
Does 1/2-20 use the same tap drill?
No. 1/2-20 UNF is a finer thread and has a different tap drill recommendation. The nominal half-inch diameter alone is not enough to choose the hole size.