Shop reference tools
Tap Drill Chart
Look up recommended tap drill sizes for UNC, UNF, and metric threads.
Tap Drill Chart lookup
Start with the table, then use the related pages for tapping, clearance holes, pilot holes, and printable shop sheets.
| Thread | Tap drill | Decimal inch | Millimeters | Working note |
|---|---|---|---|---|
| #4-40 UNC | #43 | 0.0890 | 2.26 | Common machine-screw tap size. |
| #6-32 UNC | #36 | 0.1065 | 2.71 | Useful for light machine screws. |
| #8-32 UNC | #29 | 0.1360 | 3.45 | Check thin material and thread depth. |
| #10-24 UNC | #25 | 0.1495 | 3.80 | Coarse #10 machine screw thread. |
| #10-32 UNF | #21 | 0.1590 | 4.04 | Fine #10 machine screw thread. |
| 1/4-20 UNC | #7 | 0.2010 | 5.11 | Common quarter-inch coarse tap. |
| 1/4-28 UNF | #3 | 0.2130 | 5.41 | Fine quarter-inch tap. |
| 5/16-18 UNC | F | 0.2570 | 6.53 | Coarse 5/16 inch tap. |
| 5/16-24 UNF | I | 0.2720 | 6.91 | Fine 5/16 inch tap. |
| 3/8-16 UNC | 5/16 | 0.3125 | 7.94 | Common coarse 3/8 inch tap. |
| 3/8-24 UNF | Q | 0.3320 | 8.43 | Fine 3/8 inch tap. |
| 1/2-13 UNC | 27/64 | 0.4219 | 10.72 | Coarse half-inch tap. |
| 1/2-20 UNF | 29/64 | 0.4531 | 11.51 | Fine half-inch tap. |
| M3 x 0.5 | 2.5 mm | 0.0984 | 2.50 | Approximate metric tap drill: major diameter minus pitch. |
| M4 x 0.7 | 3.3 mm | 0.1299 | 3.30 | Use published chart for production work. |
| M5 x 0.8 | 4.2 mm | 0.1654 | 4.20 | Common metric coarse thread. |
| M6 x 1 | 5.0 mm | 0.1969 | 5.00 | Common metric coarse thread. |
| M8 x 1.25 | 6.8 mm | 0.2677 | 6.80 | Common metric coarse thread. |
| M10 x 1.5 | 8.5 mm | 0.3346 | 8.50 | Common metric coarse thread. |
| M12 x 1.75 | 10.2 mm | 0.4016 | 10.20 | Common metric coarse thread. |
What is a tap drill chart?
A tap drill chart connects a thread callout, such as 1/4-28 UNF or M10 x 1.5, to a starting drill size. The best chart also shows the decimal inch value, millimeter value, and enough context to avoid mixing thread families.
How do I use a tap drill chart?
Read the full thread callout first, choose the chart row, then confirm whether the job uses a cutting tap, forming tap, controlled thread percentage, coating, or a drawing-specified drill.
What percent thread should I use for tapping?
Many simple charts assume a high thread percentage, while toolmakers often recommend lower percentages for easier tapping and longer tool life. For critical work, use the calculator and tooling guidance rather than treating one chart value as universal.
Metric, UNC, and UNF charts do not use the same labels
Metric threads use diameter and pitch. Inch threads use diameter and threads per inch. Fine-thread UNF sizes often need a different drill than the same nominal diameter in UNC.
Common tap drill sizes worth checking first
Use these common rows as entry points, then confirm the full thread callout before opening the chart or calculator.