Tap drill answer
What Size Drill Bit for 5/16-18 UNC Tap?
For a 5/16-18 UNC tap, a common reference drill is F, which is 0.2570 in or 6.53 mm. Verify the value for material, tap type, and required thread engagement.
5/16-18 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 5/16-18 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 for 5/16-18 tap?
A common chart value for a 5/16-18 UNC tap is an F drill, which is 0.2570 in or about 6.53 mm. Users often search this more generally as 5/16 tap drill size.
5/16-18 tap drill size in decimal inches
The F drill decimal is 0.2570 in. That decimal is useful when checking whether a nearby fractional or metric bit is close enough for the job.
Is 5/16-18 the same tap drill as 5/16-24?
No. 5/16-18 UNC commonly uses F, while 5/16-24 UNF commonly uses I. Coarse and fine threads at the same nominal diameter do not use the same tap drill.
5/16 tap drill size in mm
The F drill converts to about 6.53 mm. Compare that with your available metric drills and verify the final choice against thread engagement needs.