Stud bolt & heavy hex nut size chart
ASME B16.5 flanges use ASTM A193 stud bolts with A194 heavy hex nuts. Up to 1 in diameter the thread is UNC; from 1-1/8 in upward it is 8UN (8 threads per inch).
| Stud diameter | Diameter mm | Thread | Heavy hex nut A/F (spanner) | Tensile stress area |
|---|---|---|---|---|
| 1/2" | 12.7 | 13 UNC | 0.875" (22.2 mm) | 0.142 in² (92 mm²) |
| 5/8" | 15.9 | 11 UNC | 1.062" (27.0 mm) | 0.226 in² (146 mm²) |
| 3/4" | 19.0 | 10 UNC | 1.250" (31.8 mm) | 0.334 in² (216 mm²) |
| 7/8" | 22.2 | 9 UNC | 1.438" (36.5 mm) | 0.462 in² (298 mm²) |
| 1" | 25.4 | 8 UNC | 1.625" (41.3 mm) | 0.606 in² (391 mm²) |
| 1-1/8" | 28.6 | 8 8UN | 1.812" (46.0 mm) | 0.790 in² (510 mm²) |
| 1-1/4" | 31.8 | 8 8UN | 2.000" (50.8 mm) | 1.000 in² (645 mm²) |
| 1-3/8" | 34.9 | 8 8UN | 2.188" (55.6 mm) | 1.234 in² (796 mm²) |
| 1-1/2" | 38.1 | 8 8UN | 2.375" (60.3 mm) | 1.492 in² (962 mm²) |
| 1-5/8" | 41.3 | 8 8UN | 2.562" (65.1 mm) | 1.775 in² (1145 mm²) |
| 1-3/4" | 44.4 | 8 8UN | 2.750" (69.8 mm) | 2.082 in² (1343 mm²) |
| 1-7/8" | 47.6 | 8 8UN | 2.938" (74.6 mm) | 2.414 in² (1557 mm²) |
| 2" | 50.8 | 8 8UN | 3.125" (79.4 mm) | 2.771 in² (1788 mm²) |
Which flanges use which stud size
| 1/2" | 1" #150, 1-1/2" #150, 1-1/4" #150, 1/2" #150, 3/4" #150, 1/2" #300 |
| 5/8" | 2" #150, 2-1/2" #150, 3" #150, 3-1/2" #150, 4" #150, 1" #300, 1-1/4" #300, 2" #300, 3/4" #300 |
| 3/4" | 5" #150, 6" #150, 8" #150, 1-1/2" #300, 2-1/2" #300, 3" #300, 3-1/2" #300, 4" #300, 5" #300, 6" #300 |
| 7/8" | 10" #150, 12" #150, 8" #300 |
| 1" | 14" #150, 16" #150, 10" #300 |
| 1-1/8" | 18" #150, 20" #150, 12" #300, 14" #300 |
| 1-1/4" | 24" #150, 16" #300, 18" #300, 20" #300 |
| 1-1/2" | 24" #300 |
Frequently asked questions
What spanner size fits a 3/4 inch heavy hex nut?
1-1/4 in (31.8 mm) across flats.
Why are flange studs above 1 inch 8 threads per inch?
ASME B16.5 specifies the 8-thread series (8UN) for bolting 1-1/8 in and larger to ease tightening and reduce thread stripping.
How is heavy hex nut size calculated?
Width across flats = 1.5 × bolt diameter + 1/8 in (ASME B18.2.2).
Last updated 2026-11-02