← Engineering tools
Thread & Tap Drill Chart
Tap drill sizes, clearance holes, and thread dimensions for UNC, UNF, and Metric threads.
| Size | Major Ø (in) | TPI | Tap Drill | Tap Ø (in) | Close Fit (in) | Free Fit (in) |
|---|---|---|---|---|---|---|
| #1 | 0.0730 | 64 | #53 drill | 0.0595 | 0.078 | 0.082 |
| #2 | 0.0860 | 56 | #50 drill | 0.0700 | 0.094 | 0.096 |
| #3 | 0.0990 | 48 | #47 drill | 0.0785 | 0.104 | 0.110 |
| #4 | 0.1120 | 40 | #43 drill | 0.0890 | 0.116 | 0.122 |
| #5 | 0.1250 | 40 | #38 drill | 0.1015 | 0.129 | 0.136 |
| #6 | 0.1380 | 32 | #36 drill | 0.1065 | 0.144 | 0.150 |
| #8 | 0.1640 | 32 | #29 drill | 0.1360 | 0.170 | 0.177 |
| #10 | 0.1900 | 24 | #25 drill | 0.1495 | 0.196 | 0.204 |
| #12 | 0.2160 | 24 | #16 drill | 0.1770 | 0.221 | 0.228 |
| 1/4 | 0.2500 | 20 | #7 drill | 0.2010 | 0.257 | 0.266 |
| 5/16 | 0.3125 | 18 | F drill | 0.2570 | 0.323 | 0.332 |
| 3/8 | 0.3750 | 16 | 5/16" | 0.3125 | 0.386 | 0.397 |
| 7/16 | 0.4375 | 14 | U drill | 0.3680 | 0.453 | 0.469 |
| 1/2 | 0.5000 | 13 | 27/64" | 0.4219 | 0.516 | 0.531 |
| 9/16 | 0.5625 | 12 | 31/64" | 0.4844 | 0.578 | 0.594 |
| 5/8 | 0.6250 | 11 | 17/32" | 0.5313 | 0.641 | 0.656 |
| 3/4 | 0.7500 | 10 | 21/32" | 0.6563 | 0.766 | 0.781 |
| 7/8 | 0.8750 | 9 | 49/64" | 0.7656 | 0.891 | 0.906 |
| 1 | 1.0000 | 8 | 7/8" | 0.8750 | 1.016 | 1.031 |
Notes
- Tap Drill — Drill size for ~75% thread engagement with cutting taps. Forming (roll) taps need a larger hole — use the tap maker's chart. Number/letter drills are designations, not dimensions.
- Close Fit — Minimum clearance hole (bolt fits with minimal play)
- Free Fit — Standard clearance hole (easy assembly). Inch clearances follow the Machinery's Handbook close/free drill table; metric follow ISO 273 medium series.
- For softer materials or deep holes, consider 60-65% thread engagement (larger tap drill)
About this tool
Looks up tap-drill and clearance-hole sizes for common UNC/UNF and ISO metric threads, with thread percentage guidance.
- Inputs
- Thread standard and designation
- Thread percentage (for cut taps)
- Assumptions
- Cut (not form) taps unless stated — forming taps use a larger drill
- 75% thread engagement as the default for general-purpose work
- Nominal sizes; no tolerance-class analysis
- Sources
- ASME B1.1 and B1.13M thread standards
- Standard tap-drill charts from tap manufacturers
- Valid range
- #0–1 in UNC/UNF; M1.6–M24 coarse and common fine pitches.
- Limitations
- Does not cover pipe threads, Acme, or specialty forms
- Clearance holes are one common class; check the applicable drawing standard
- Material and hole depth affect the right thread percentage
Values are starting points for planning — verify against your tooling and machine documentation before cutting. Report an issue with this tool →