5/16-24 Tap Drill Size & Thread Specs
Everything for a 5/16-24 UNF thread on one page: tap drill (I), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · 5/16-24
5/16-24 specs
SizePlate
5/16-24 UNF · tap with
I drill
.2720″
6.91 mm · 75% thread
- Metric drill
- 6.9 mm · .2717
- Clearance
- P / Q
- Wrench
- 1/2″
- Cap screw key
- 1/4″
Thread
- Nominal size
- 5/16″ · 7.94 mm
- Major diameter
- .3125″
- Threads per inch
- 24
- Pitch
- .0417″ · 1.058 mm
- Series
- UNF (fine)
- UNC version
- 5/16-18
Drilling
- Tap drill (75%)
- I · .2720
- Metric substitute
- 6.9 mm · .2717
- Tap drill (≈50%)
- 9/32 · .2813
- Close fit
- P · .3230
- Free fit
- Q · .3320
Tools
- Hex bolt wrench
- 1/2″
- Hex nut wrench
- 1/2″
- Socket head cap key
- 1/4″
- Button head key
- 3/16″
- Flat head key
- 3/16″
Nearest metric
- Thread
- M8 × 1.25
- Major diameter
- 8 mm
- Pitch
- 1.25 mm
- Tap drill
- 6.8 mm
- Interchangeable
- No
Not interchangeable means the threads look close but won't run together: forcing one into the other strips both.
Drill size by thread percentage
Larger drill, less thread, easier tapping. 75% is the usual target.
| Drill | Decimal | mm | Thread |
|---|---|---|---|
| 6.8 mm | .2677 | 6.8 | 83% |
| 6.9 mm | .2717 | 6.9 | 75% |
| I | .2720 | 6.91 | 75% |
| 7 mm | .2756 | 7 | 68% |
| J | .2770 | 7.04 | 66% |
| 7.1 mm | .2795 | 7.1 | 61% |
| K | .2810 | 7.14 | 58% |
| 9/32 | .2813 | 7.15 | 58% |
| 7.2 mm | .2835 | 7.2 | 54% |
| 7.3 mm | .2874 | 7.3 | 46% |
Neighboring sizes
Questions
What does 5/16-24 mean?
A 5/16″ nominal diameter with 24 threads per inch. It’s the fine (UNF) thread for that size; the coarse version is 5/16-18.
Can I use a 6.9 mm drill instead of I?
Usually. 6.9 mm is .2717″ against .2720″ for I, which changes the thread engagement by a few percent at most. The thread-percentage table above shows exactly how much thread each nearby drill leaves.