UNC and ISO metric coarse threads
| Diameter (in) | Threads per inch | Nominal area (in²) | Tensile stress area (in²) | As (mm²) |
|---|---|---|---|---|
| 1/4 | 20 | 0.0491 | 0.0318 | 20.5 |
| 5/16 | 18 | 0.0767 | 0.0524 | 33.8 |
| 3/8 | 16 | 0.1104 | 0.0775 | 50.0 |
| 7/16 | 14 | 0.1503 | 0.1063 | 68.6 |
| 1/2 | 13 | 0.1963 | 0.1419 | 91.5 |
| 9/16 | 12 | 0.2485 | 0.1819 | 117.4 |
| 5/8 | 11 | 0.3068 | 0.2260 | 145.8 |
| 3/4 | 10 | 0.4418 | 0.3345 | 215.8 |
| 7/8 | 9 | 0.6013 | 0.4617 | 297.9 |
| 1 | 8 | 0.7854 | 0.6057 | 390.8 |
| 1-1/8 | 7 | 0.9940 | 0.7633 | 492.4 |
| 1-1/4 | 7 | 1.2272 | 0.9691 | 625.2 |
| 1-3/8 | 6 | 1.4849 | 1.1549 | 745.1 |
| 1-1/2 | 6 | 1.7671 | 1.4053 | 906.6 |
As = 0.7854 (d − 0.9743/n)² per ASME B1.1.
| Size | Pitch (mm) | Nominal area (mm²) | Tensile stress area (mm²) | As (in²) |
|---|---|---|---|---|
| M6 | 1 | 28.3 | 20.1 | 0.031 |
| M8 | 1.25 | 50.3 | 36.6 | 0.057 |
| M10 | 1.5 | 78.5 | 58.0 | 0.090 |
| M12 | 1.75 | 113.1 | 84.3 | 0.131 |
| M14 | 2 | 153.9 | 115.4 | 0.179 |
| M16 | 2 | 201.1 | 156.7 | 0.243 |
| M20 | 2.5 | 314.2 | 244.8 | 0.379 |
| M22 | 2.5 | 380.1 | 303.4 | 0.470 |
| M24 | 3 | 452.4 | 352.5 | 0.546 |
| M27 | 3 | 572.6 | 459.4 | 0.712 |
| M30 | 3.5 | 706.9 | 560.6 | 0.869 |
| M36 | 4 | 1,017.9 | 816.7 | 1.266 |
As = (π/4)(d − 0.9382 P)² per ISO 898-1. Coarse pitch per ISO 261.
| Grade | Min. tensile strength | AISC Fnt |
|---|---|---|
| ASTM A307 Gr. A | 60 ksi | 45 ksi |
| ASTM F3125 Gr. A325 | 120 ksi | 90 ksi |
| ASTM F3125 Gr. A490 | 150 ksi | 113 ksi |
| ISO class 8.8 | 800 MPa (830 MPa above M16) | n/a |
| ISO class 10.9 | 1,040 MPa | n/a |
Fnt is the AISC 360 nominal tensile stress, applied to the nominal body area.
The effective area of the threaded section used to compute bolt tensile strength. For UNC threads, As = 0.7854 (d − 0.9743/n)² with d in inches and n threads per inch.
0.334 in² for 3/4-10 UNC. The nominal (shank) area is 0.442 in², so the threads remove about 25% of the area.
No. AISC 360 uses the nominal body area Ab = πd²/4 with a reduced nominal stress (Fnt = 0.75 Fu) that already accounts for the threads. Machine design and ISO calculations use As directly.
ISO 898-1: As = (π/4)(d − 0.9382 P)², with d the nominal diameter and P the thread pitch in mm. An M20 × 2.5 bolt has As = 245 mm².