Tap drill answer
What Size Drill Bit for 3/8-16 UNC Tap?
For a 3/8-16 UNC tap, a common reference drill is 5/16, which is 0.3125 in or 7.94 mm. Verify the value for material, tap type, and required thread engagement.
3/8-16 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 3/8-16 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 3/8-16 tap?
A common chart value for a 3/8-16 UNC tap is 5/16 in, which is 0.3125 in or about 7.94 mm. Confirm that the thread is the 16 TPI coarse series before using this row.
Is 5/16 the standard 3/8-16 tap drill?
5/16 in is the common cutting-tap starting point in general charts. A forming tap, controlled thread percentage, hard material, or drawing requirement can call for a different hole.
What is the 3/8-16 tap drill size in millimeters?
5/16 in converts to 7.94 mm. Compare the exact decimal with the available metric drill instead of assuming every 8 mm bit creates the same thread engagement.
Does 3/8-24 use the same tap drill?
No. 3/8-16 UNC and 3/8-24 UNF have different pitches and normally use different tap drills. Read the complete thread callout before drilling.