#5-40 Tap Drill Size & Thread Specs
Everything for a #5-40 UNC thread on one page: tap drill (#38), clearance holes, wrench and hex key sizes, and the nearest metric thread.
SP-TD-01 · #5-40
#5-40 specs
SizePlate
#5-40 UNC · tap with
#38 drill
.1015″
2.58 mm · 72% thread
- Metric drill
- 2.6 mm · .1024
- Clearance
- #30 / #29
Thread
- Nominal size
- #5 · 3.17 mm
- Major diameter
- .1250″
- Threads per inch
- 40
- Pitch
- .0250″ · 0.635 mm
- Series
- UNC (coarse)
- UNF version
- #5-44
Drilling
- Tap drill (75%)
- #38 · .1015
- Metric substitute
- 2.6 mm · .1024
- Tap drill (≈50%)
- 7/64 · .1094
- Close fit
- #30 · .1285
- Free fit
- #29 · .1360
Nearest metric
- Thread
- M3 × 0.5
- Major diameter
- 3 mm
- Pitch
- 0.5 mm
- Tap drill
- 2.5 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 |
|---|---|---|---|
| #40 | .0980 | 2.49 | 83% |
| 2.5 mm | .0984 | 2.5 | 82% |
| #39 | .0995 | 2.53 | 79% |
| #38 | .1015 | 2.58 | 72% |
| 2.6 mm | .1024 | 2.6 | 70% |
| #37 | .1040 | 2.64 | 65% |
| 2.65 mm | .1043 | 2.65 | 64% |
| 2.7 mm | .1063 | 2.7 | 58% |
| #36 | .1065 | 2.71 | 57% |
| 7/64 | .1094 | 2.78 | 48% |
| #35 | .1100 | 2.79 | 46% |
| 2.8 mm | .1102 | 2.8 | 45% |
Neighboring sizes
Questions
What does #5-40 mean?
A #5 nominal diameter with 40 threads per inch. It’s the coarse (UNC) thread for that size; the fine version is #5-44.
Can I use a 2.6 mm drill instead of #38?
Usually. 2.6 mm is .1024″ against .1015″ for #38, 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.