Tap drill answer
What Size Drill Bit for 1/4-28 UNF Tap?
For a 1/4-28 UNF tap, a common reference drill is #3, which is 0.2130 in or 5.41 mm. Verify the value for material, tap type, and required thread engagement.
1/4-28 UNF 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 1/4-28 UNF 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 size drill bit for 1/4-28 UNF tap?
A common chart value for a 1/4-28 UNF tap is a #3 drill, which is 0.2130 in or about 5.41 mm. Many searchers also compare this with 7/32 in because it is close and easy to find, but the named chart drill is still the better starting point.
Is #3 the right drill for 1/4-28?
#3 is the standard reference value used by many inch tap drill charts. If the drawing, tap maker, material, or thread percentage calls for something else, follow that source instead of forcing the chart value.
What is 1/4-28 tap drill size in mm?
The #3 drill is 0.2130 in, which converts to about 5.41 mm. Some metric product listings round to 5.5 mm, so check whether the listing is giving a practical kit size or the exact chart decimal.
1/4-28 UNF vs 1/4-20 UNC tap drill size
Do not use the coarse-thread 1/4-20 drill for 1/4-28. The fine-thread 1/4-28 UNF row commonly uses #3, while 1/4-20 UNC commonly uses #7.