UNC Thread Chart (Unified Coarse)
All 33 Unified coarse threads from #1-64 to 4-4, with diameters, tap drill and tensile stress area. UNC is the default inch thread: a bolt described only by its diameter, such as a 1/2 inch bolt, is normally 1/2-13 UNC.
| Thread | TPI | Major Ø (in) | Pitch Ø (in) | Minor Ø D1 (in) | Tap drill | Drill (in) | Drill (mm) | % thread | Stress area (in²) |
|---|---|---|---|---|---|---|---|---|---|
| #1-64 UNC | 64 | 0.0730 | 0.0629 | 0.0561 | #53 | 0.0595 | 1.51 | 67% | 0.00263 |
| #2-56 UNC | 56 | 0.0860 | 0.0744 | 0.0667 | #50 | 0.0700 | 1.78 | 69% | 0.00370 |
| #3-48 UNC | 48 | 0.0990 | 0.0855 | 0.0764 | #47 | 0.0785 | 1.99 | 76% | 0.00487 |
| #4-40 UNC | 40 | 0.1120 | 0.0958 | 0.0849 | #43 | 0.0890 | 2.26 | 71% | 0.00604 |
| #5-40 UNC | 40 | 0.1250 | 0.1088 | 0.0979 | #38 | 0.1015 | 2.58 | 72% | 0.00796 |
| #6-32 UNC | 32 | 0.1380 | 0.1177 | 0.1042 | #36 | 0.1065 | 2.71 | 78% | 0.00909 |
| #8-32 UNC | 32 | 0.1640 | 0.1437 | 0.1302 | #29 | 0.1360 | 3.45 | 69% | 0.0140 |
| #10-24 UNC | 24 | 0.1900 | 0.1629 | 0.1449 | #25 | 0.1495 | 3.80 | 75% | 0.0175 |
| #12-24 UNC | 24 | 0.2160 | 0.1889 | 0.1709 | #16 | 0.1770 | 4.50 | 72% | 0.0242 |
| 1/4-20 UNC | 20 | 0.2500 | 0.2175 | 0.1959 | #7 | 0.2010 | 5.11 | 75% | 0.0318 |
| 5/16-18 UNC | 18 | 0.3125 | 0.2764 | 0.2524 | F | 0.2570 | 6.53 | 77% | 0.0524 |
| 3/8-16 UNC | 16 | 0.3750 | 0.3344 | 0.3073 | 5/16" | 0.3125 | 7.94 | 77% | 0.0775 |
| 7/16-14 UNC | 14 | 0.4375 | 0.3911 | 0.3602 | U | 0.3680 | 9.35 | 75% | 0.1063 |
| 1/2-13 UNC | 13 | 0.5000 | 0.4500 | 0.4167 | 27/64" | 0.4219 | 10.72 | 78% | 0.1419 |
| 9/16-12 UNC | 12 | 0.5625 | 0.5084 | 0.4723 | 31/64" | 0.4844 | 12.30 | 72% | 0.182 |
| 5/8-11 UNC | 11 | 0.6250 | 0.5660 | 0.5266 | 17/32" | 0.5312 | 13.49 | 79% | 0.226 |
| 3/4-10 UNC | 10 | 0.7500 | 0.6850 | 0.6417 | 21/32" | 0.6562 | 16.67 | 72% | 0.334 |
| 7/8-9 UNC | 9 | 0.8750 | 0.8028 | 0.7547 | 49/64" | 0.7656 | 19.45 | 76% | 0.462 |
| 1-8 UNC | 8 | 1.0000 | 0.9188 | 0.8647 | 7/8" | 0.8750 | 22.22 | 77% | 0.606 |
| 1-1/8-7 UNC | 7 | 1.1250 | 1.0322 | 0.9704 | 63/64" | 0.9844 | 25.00 | 76% | 0.763 |
| 1-1/4-7 UNC | 7 | 1.2500 | 1.1572 | 1.0954 | 1-7/64" | 1.1094 | 28.18 | 76% | 0.969 |
| 1-3/8-6 UNC | 6 | 1.3750 | 1.2667 | 1.1946 | 1-7/32" | 1.2188 | 30.96 | 72% | 1.155 |
| 1-1/2-6 UNC | 6 | 1.5000 | 1.3917 | 1.3196 | 1-11/32" | 1.3438 | 34.13 | 72% | 1.405 |
| 1-3/4-5 UNC | 5 | 1.7500 | 1.6201 | 1.5335 | 1-9/16" | 1.5625 | 39.69 | 72% | 1.9 |
| 2-4.5 UNC | 4.5 | 2.0000 | 1.8557 | 1.7594 | 1-25/32" | 1.7812 | 45.24 | 76% | 2.5 |
| 2-1/4-4.5 UNC | 4.5 | 2.2500 | 2.1057 | 2.0094 | 2-1/32" | 2.0312 | 51.59 | 76% | 3.25 |
| 2-1/2-4 UNC | 4 | 2.5000 | 2.3376 | 2.2294 | 2-1/4" | 2.2500 | 57.15 | 77% | 4 |
| 2-3/4-4 UNC | 4 | 2.7500 | 2.5876 | 2.4794 | 2-1/2" | 2.5000 | 63.50 | 77% | 4.93 |
| 3-4 UNC | 4 | 3.0000 | 2.8376 | 2.7294 | 2-3/4" | 2.7500 | 69.85 | 77% | 5.97 |
| 3-1/4-4 UNC | 4 | 3.2500 | 3.0876 | 2.9794 | 3" | 3.0000 | 76.20 | 77% | 7.1 |
| 3-1/2-4 UNC | 4 | 3.5000 | 3.3376 | 3.2294 | 3-1/4" | 3.2500 | 82.55 | 77% | 8.33 |
| 3-3/4-4 UNC | 4 | 3.7500 | 3.5876 | 3.4794 | 3-1/2" | 3.5000 | 88.90 | 77% | 9.66 |
| 4-4 UNC | 4 | 4.0000 | 3.8376 | 3.7294 | 3-3/4" | 3.7500 | 95.25 | 77% | 11.08 |
About the UNC series
The coarse series has the fewest threads per inch that ASME B1.1 assigns to each diameter. The threads are deep relative to the diameter, which makes them quick to assemble, tolerant of dirt, burrs and plating, and strong in soft materials such as cast iron and aluminium, where the nut thread is the weak part of the joint.
The series starts at #1. There is no #0 coarse thread: #0-80 belongs to the fine series. Above 1 inch, the 8-thread series (8 UN) is often used in place of UNC for high-pressure bolting, because its pitch stays constant as the diameter grows.
Threads per inch by series
Common questions
What is the tap drill for 1/4-20?
The tap drill for 1/4-20 UNC is a #7 drill, 0.2010 in (5.11 mm). It leaves about 75% thread.
What is the tap drill for 3/8-16?
The tap drill for 3/8-16 UNC is 5/16 in, 0.3125 in (7.94 mm), for about 77% thread.
What does 1/4-20 mean?
The first number is the major diameter in inches and the second is the number of threads per inch. 1/4-20 is a 0.250 in thread with 20 threads per inch, a pitch of 0.050 in.
Other charts and tools
Sources: ASME B1.1 (series, basic dimensions and stress areas) and the tap drill tables of Machinery’s Handbook. How this site checks its data. Last reviewed 29 September 2026.