Tap drill answer
What Size Drill Bit for 1/4-20 UNC Tap?
For a 1/4-20 UNC tap, a common reference drill is #7, which is 0.2010 in or 5.11 mm. Verify the value for material, tap type, and required thread engagement.
1/4-20 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 1/4-20 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 size drill bit for 1/4-20 tap?
A common chart value for a 1/4-20 UNC tap is a #7 drill, which is 0.2010 in or about 5.11 mm. The spacing and punctuation in a thread callout may vary, but the diameter and 20 TPI must both match before using this row.
Is #7 the right drill for 1/4-20?
#7 is the standard starting point on many hand-tapping charts. If your drawing specifies a thread percentage, forming tap, coating allowance, or special material, follow that source instead of treating #7 as universal.
What is 1/4-20 tap drill size in mm?
The #7 drill is 0.2010 in, which converts to about 5.11 mm. A nearby metric drill may be convenient for rough work, but the named chart drill is the reference value to compare against.
1/4-20 UNC vs 1/4-28 UNF tap drill size
1/4-20 UNC commonly uses #7. 1/4-28 UNF commonly uses #3. The nominal diameter is the same, but the thread pitch changes the tap drill.