Thread Specifications & Tap Drill Reference
Complete reference for 207 thread specifications — ISO metric, UNC, UNF, UNEF, NPT, and BSP. All dimensions calculated from ISO 724 and ASME B1.1 formulas.
ISO Metric Threads
36 coarse + 56 fine pitch sizes. M1 to M68 with complete dimensions and tap drills.
Unified Inch Threads
33 UNC + 24 UNF + 22 UNEF sizes. #0 to 4" with inch and metric dimensions.
Pipe Threads
19 NPT + 17 BSP sizes. Tapered and parallel pipe thread specifications.
Tap Drill Chart
Complete tap drill sizes for all thread standards in mm and inches.
Thread Calculator
Calculate thread dimensions, tap drills, and stress areas for any pitch and diameter.
NPT vs BSP
Side-by-side comparison of NPT and BSP pipe thread standards.
Popular Metric Thread Sizes
| Thread | Pitch (mm) | Major Ø (mm) | Pitch Ø (mm) | Tap Drill (mm) | Stress Area (mm²) |
|---|---|---|---|---|---|
| M3 | 0.5 | 3 | 2.675 | 2.46 | 4.9 |
| M4 | 0.7 | 4 | 3.545 | 3.24 | 8.5 |
| M5 | 0.8 | 5 | 4.48 | 4.13 | 13.8 |
| M6 | 1.0 | 6 | 5.351 | 4.92 | 19.6 |
| M8 | 1.25 | 8 | 7.188 | 6.65 | 35.6 |
| M10 | 1.5 | 10 | 9.026 | 8.38 | 56.5 |
| M12 | 1.75 | 12 | 10.863 | 10.11 | 82.2 |
| M16 | 2.0 | 16 | 14.701 | 13.84 | 153.5 |
| M20 | 2.5 | 20 | 18.376 | 17.29 | 239.8 |
| M24 | 3.0 | 24 | 22.052 | 20.75 | 345.3 |
Popular UNC Thread Sizes
| Thread | Major Ø (in) | Pitch Ø (in) | Minor Ø (in) | Tap Drill (mm) |
|---|---|---|---|---|
| #6-32 UNC | 0.138 | 0.1177 | 0.0997 | 2.6 |
| #8-32 UNC | 0.164 | 0.1437 | 0.1257 | 3.3 |
| #10-24 UNC | 0.19 | 0.1629 | 0.1389 | 3.7 |
| 1/4-20 UNC | 0.25 | 0.2175 | 0.1887 | 5 |
| 5/16-18 UNC | 0.3125 | 0.2764 | 0.2443 | 6.4 |
| 3/8-16 UNC | 0.375 | 0.3344 | 0.2983 | 7.8 |
| 1/2-13 UNC | 0.5 | 0.45 | 0.4056 | 10.6 |
| 5/8-11 UNC | 0.625 | 0.566 | 0.5135 | 13.4 |
| 3/4-10 UNC | 0.75 | 0.6851 | 0.6273 | 16.3 |
| 1-8 UNC | 1 | 0.9188 | 0.8466 | 22 |
About ThreadSpec.org
ThreadSpec.org is a comprehensive thread specification reference built for engineers, machinists, and makers. Every dimension on this site is calculated directly from published engineering formulas — ISO 724 for metric threads and ASME B1.1 for unified inch threads — not copied from other sources.
Our database covers 207 thread specifications across six major standards: ISO Metric (coarse and fine), UNC, UNF, UNEF, NPT, and BSP. Each thread page includes major, pitch, and minor diameters, tap drill sizes, tensile stress areas, and proof loads for common material grades.