Complete thread pitch reference for UNC, UNF, UNEF, and metric threads. Major diameter, minor diameter, pitch diameter, and tap drill for every standard thread size.
Last updated April 2026
| Designation↑ | TPI↕ | Major Dia | Minor Dia | Pitch Dia | Tap Drill | Class |
|---|---|---|---|---|---|---|
| #1-64 UNC | 64 | 0.0730" | 0.0538" | 0.0629" | #53 | Class 2B |
| #2-56 UNC | 56 | 0.0860" | 0.0641" | 0.0744" | #50 | Class 2B |
| #3-48 UNC | 48 | 0.0990" | 0.0734" | 0.0855" | #47 | Class 2B |
| #4-40 UNC | 40 | 0.1120" | 0.0813" | 0.0958" | #43 | Class 2B |
| #5-40 UNC | 40 | 0.1250" | 0.0943" | 0.1088" | #38 | Class 2B |
| #6-32 UNC | 32 | 0.1380" | 0.0997" | 0.1177" | #36 | Class 2B |
| #8-32 UNC | 32 | 0.1640" | 0.1257" | 0.1437" | #29 | Class 2B |
| #10-24 UNC | 24 | 0.1900" | 0.1389" | 0.1629" | #25 | Class 2B |
| #12-24 UNC | 24 | 0.2160" | 0.1649" | 0.1889" | #16 | Class 2B |
| 1/4"-20 UNC | 20 | 0.2500" | 0.1887" | 0.2175" | #7 | Class 2B |
| 5/16"-18 UNC | 18 | 0.3125" | 0.2443" | 0.2764" | F | Class 2B |
| 3/8"-16 UNC | 16 | 0.3750" | 0.2983" | 0.3344" | 5/16 | Class 2B |
| 7/16"-14 UNC | 14 | 0.4375" | 0.3499" | 0.3911" | U | Class 2B |
| 1/2"-13 UNC | 13 | 0.5000" | 0.4056" | 0.4500" | 27/64 | Class 2B |
| 9/16"-12 UNC | 12 | 0.5625" | 0.4603" | 0.5084" | 31/64 | Class 2B |
| 5/8"-11 UNC | 11 | 0.6250" | 0.5135" | 0.5660" | 17/32 | Class 2B |
| 3/4"-10 UNC | 10 | 0.7500" | 0.6273" | 0.6850" | 21/32 | Class 2B |
| 7/8"-9 UNC | 9 | 0.8750" | 0.7387" | 0.8028" | 49/64 | Class 2B |
| 1"-8 UNC | 8 | 1.0000" | 0.8466" | 0.9188" | 7/8 | Class 2B |
| 1-1/8"-7 UNC | 7 | 1.1250" | 0.9497" | 1.0322" | 63/64 | Class 2B |
| 1-1/4"-7 UNC | 7 | 1.2500" | 1.0747" | 1.1572" | 1-7/64 | Class 2B |
| 1-3/8"-6 UNC | 6 | 1.3750" | 1.1705" | 1.2667" | 1-13/64 | Class 2B |
| 1-1/2"-6 UNC | 6 | 1.5000" | 1.2955" | 1.3917" | 1-11/32 | Class 2B |
| 1-3/4"-5 UNC | 5 | 1.7500" | 1.5046" | 1.6201" | 1-35/64 | Class 2B |
| 2"-4.5 UNC | 4.5 | 2.0000" | 1.7353" | 1.8602" | 1-25/32 | Class 2B |
Thread pitch is the distance between adjacent thread crests. For imperial threads it is expressed as threads per inch (TPI). For metric threads it is the distance in millimeters between threads.
Pitch diameter is the theoretical diameter where the thread tooth width equals the space between threads. It is the most important dimension for thread fit and is measured between the 50% points of the thread flanks.