Inch Tap Drill Chart (1/4 to 7/8, UNC and UNF)
Fractional inch threads from 1/4 to 7/8, coarse (UNC) and fine (UNF). A fine thread takes a larger drill than the coarse thread of the same diameter.
| Thread | Series | Major diameter | Pitch | Aluminum, brass (75%) | Mild steel (60%) | Stainless, titanium (50%) |
|---|---|---|---|---|---|---|
| 1/4-20 | UNC | 0.2500 in (6.35 mm) | 20 TPI (1.270 mm) | #7 75% | #4 63% | 7/32 in 48% |
| 5/16-18 | UNC | 0.3125 in (7.94 mm) | 18 TPI (1.411 mm) | letter F 77% | letter H 64% | letter J 49% |
| 3/8-16 | UNC | 0.3750 in (9.52 mm) | 16 TPI (1.587 mm) | 5/16 in 77% | letter P 64% | letter Q 53% |
| 7/16-14 | UNC | 0.4375 in (11.11 mm) | 14 TPI (1.814 mm) | letter U 75% | letter V 65% | 25/64 in 51% |
| 1/2-13 | UNC | 0.5000 in (12.70 mm) | 13 TPI (1.954 mm) | 27/64 in 78% | 7/16 in 63% | 29/64 in 47% |
| 9/16-12 | UNC | 0.5625 in (14.29 mm) | 12 TPI (2.117 mm) | 31/64 in 72% | 1/2 in 58% | 1/2 in 58% |
| 5/8-11 | UNC | 0.6250 in (15.88 mm) | 11 TPI (2.309 mm) | 17/32 in 79% | 35/64 in 66% | 9/16 in 53% |
| 3/4-10 | UNC | 0.7500 in (19.05 mm) | 10 TPI (2.540 mm) | 21/32 in 72% | 43/64 in 60% | 11/16 in 48% |
| 7/8-9 | UNC | 0.8750 in (22.22 mm) | 9 TPI (2.822 mm) | 49/64 in 76% | 25/32 in 65% | 51/64 in 54% |
| 1/4-28 | UNF | 0.2500 in (6.35 mm) | 28 TPI (0.907 mm) | #3 80% | #2 63% | #1 47% |
| 5/16-24 | UNF | 0.3125 in (7.94 mm) | 24 TPI (1.058 mm) | letter I 75% | letter K 58% | 9/32 in 58% |
| 3/8-24 | UNF | 0.3750 in (9.52 mm) | 24 TPI (1.058 mm) | letter Q 79% | letter R 67% | letter S 50% |
| 7/16-20 | UNF | 0.4375 in (11.11 mm) | 20 TPI (1.270 mm) | 25/64 in 72% | letter X 62% | 13/32 in 48% |
| 1/2-20 | UNF | 0.5000 in (12.70 mm) | 20 TPI (1.270 mm) | 29/64 in 72% | 29/64 in 72% | 15/32 in 48% |
| 9/16-18 | UNF | 0.5625 in (14.29 mm) | 18 TPI (1.411 mm) | 33/64 in 65% | 33/64 in 65% | 33/64 in 65% |
| 5/8-18 | UNF | 0.6250 in (15.88 mm) | 18 TPI (1.411 mm) | 37/64 in 65% | 37/64 in 65% | 37/64 in 65% |
| 3/4-16 | UNF | 0.7500 in (19.05 mm) | 16 TPI (1.587 mm) | 11/16 in 77% | 45/64 in 58% | 45/64 in 58% |
| 7/8-14 | UNF | 0.8750 in (22.22 mm) | 14 TPI (1.814 mm) | 13/16 in 67% | 13/16 in 67% | 53/64 in 51% |
Small percentages show the thread engagement each drill leaves. Click a thread for the full page.
Inch Tap Drill Chart (1/4 to 7/8, UNC and UNF) | tapdrillsize.com/inch-tap-drill-chart/ | Last reviewed October 7, 2026 | Check your tap maker's chart before cutting.
UNC and UNF side by side
Every diameter here comes as a coarse (UNC) and a fine (UNF) thread, with a different drill for each.
| Diameter | Coarse thread | Coarse drill | Fine thread | Fine drill |
|---|---|---|---|---|
| 1/4 in (6.35 mm) | 1/4-20 | #7 | 1/4-28 | #3 |
| 5/16 in (7.94 mm) | 5/16-18 | letter F | 5/16-24 | letter I |
| 3/8 in (9.52 mm) | 3/8-16 | 5/16 in | 3/8-24 | letter Q |
| 7/16 in (11.11 mm) | 7/16-14 | letter U | 7/16-20 | 25/64 in |
| 1/2 in (12.70 mm) | 1/2-13 | 27/64 in | 1/2-20 | 29/64 in |
| 9/16 in (14.29 mm) | 9/16-12 | 31/64 in | 9/16-18 | 33/64 in |
| 5/8 in (15.88 mm) | 5/8-11 | 17/32 in | 5/8-18 | 37/64 in |
| 3/4 in (19.05 mm) | 3/4-10 | 21/32 in | 3/4-16 | 11/16 in |
| 7/8 in (22.22 mm) | 7/8-9 | 49/64 in | 7/8-14 | 13/16 in |
Why a finer thread needs a bigger drill
A full thread is 0.0325 in deep on each side at 20 threads per inch (1/4-20) and 0.0232 in deep at 28 threads per inch (1/4-28). The fine thread cuts less into the wall, so its drill is closer to the screw diameter: #7 for 1/4-20 and #3 for 1/4-28.
Fractions to decimals
1/4 in is 0.2500 in and 6.35 mm. Each diameter in the table above is shown in inches and millimetres, so you can match it to a metric drill set. Thread depth per side is 0.6495 times the pitch.
FAQ
What is the tap drill size for 3/8-16?
5/16 in (0.3125 in, 7.94 mm) leaves about 77% thread. That is the standard drill for the coarse 3/8 thread. The fine 3/8-24 takes letter Q.
What is the tap drill size for 1/2-13?
27/64 in (0.4219 in, 10.72 mm) leaves about 78% thread. The fine 1/2-20 takes 29/64 in.
What is the difference between UNC and UNF?
UNC is the coarse series and UNF is the fine series of the same Unified Thread Standard (Wikipedia). At one diameter the fine thread has more threads per inch, so it is shallower and takes a bigger drill.
What is 5/16 inch in millimetres?
5/16 in is 0.3125 in, which is 7.94 mm. The table above lists every diameter in both units.
Chart drills match the American Fastener tap and drill chart and the Fabworks tap drill chart. Thread percentages use the formula printed in the OSG tap drill chart, Vol 3 (2024). Last reviewed October 7, 2026. Method: how the numbers are calculated.