Drill Bit Size for a 5/16-24 Tap Is A Letter I Drill Bit

The drill bit size for a 5/16-24 tap is a letter I drill bit, which has a diameter of 0.2720″ (6.91 mm).

5/16-24 Drill and Tap Quick Reference

• Tap size: 5/16-24 UNF
• Tap drill size: Letter I
• Drill diameter: 0.2720"
• Metric equivalent: 6.91 mm
• Closest metric drill: 6.9 mm

Drill Bit Size for 5/16-24 Tap (Tap Drill Size)

The drill bit size for a 5/16-24 tap is a letter I drill bit. This is the standard tap drill size for 5/16-24 UNF threads. A letter I drill has a diameter of 0.2720 inches, which is the correct hole size to produce apprximately 75% thread engagement.

For common search queries such as 5 16 24 tap drill size, tap drill 5 16 24, drill bit size for 5 16 24 tap, and tap drill size for 5 16 24, the correct answer is a letter I drill bit.

Why Use a Letter I Drill for a 5/16-24 Tap

The tap drill size for a 5/16-24 thread must provide the correct balance between thread engagement and tapping performance. A letter I drill removes the proper amount of material to allow the tap to cut threads efficiently without excessive force.

Using the correct 5/16-24 tap drill size helps:

• Reduce tapping torque
• Lower the risk of broken taps
• Improve thread consistency
• Extend tool life
• Maintain proper thread fit

If a smaller drill bit is used, the tap must remove more material, which increases torque and wear. If a larger drill bit is used, thread engagement is reduced and thread strength may be compromised. The letter I drill is the correct and standard drill size for a 5/16-24 UNF tap.

Metric Drill Size for 5/16-24 Tap

A 6.9 mm drill bit is the closest metric equivalent to a letter I drill. This size can be used when a letter I drill bit is not available.  The thread percentage the 6.9mm bit produces is very close to the same as the letter I drill bit.

Common Uses for 5/16-24 Tap Drill Size

• Preparing holes for 5/16-24 UNF threads
• Machining and CNC operations
• Maintenance and repair work
• General metalworking applications
• Through holes and blind holes before tapping

The correct hole size for a 5/16-24 tap is critical for thread quality and tool performance. Using the proper tap drill size ensures consistent results across a wide range of materials and applications.

 Find I Drill Bits Below

Shop letter I drill bits in HSS, cobalt, and carbide to match your material, cutting conditions, and production requirements.