Flange Dimensions / Reference Tools
Flange Bolt Chart
Stud bolt quantities and diameters for ASME B16.5 flanges
Flange bolting is a critical element in achieving a leak-free joint. The standard bolt material for ASME B16.5 flanges in carbon steel piping systems is ASTM A193 Grade B7 stud bolts paired with ASTM A194 Grade 2H heavy hex nuts. B7 studs are made from chromium-molybdenum steel, quenched and tempered, providing a minimum tensile strength of 125,000 psi for diameters up to 2-1/2 inches. For low-temperature service, ASTM A320 Grade L7 studs are commonly specified.
The number and diameter of bolts required for a flanged joint increases with both the nominal pipe size and the pressure class. Higher pressure classes require more bolts of larger diameter to develop the gasket seating stress and resist hydrostatic end force. The table below provides the bolt quantities and diameters for Class 150, 300, and 600 flanges as specified in ASME B16.5. All dimensions are for stud bolts with two heavy hex nuts per stud.
| NPS | Cl.150 Bolts | Cl.150 Dia | Cl.300 Bolts | Cl.300 Dia | Cl.600 Bolts | Cl.600 Dia |
|---|---|---|---|---|---|---|
| 1/2 | 4 | 1/2 | 4 | 1/2 | 4 | 1/2 |
| 3/4 | 4 | 1/2 | 4 | 5/8 | 4 | 5/8 |
| 1 | 4 | 1/2 | 4 | 5/8 | 4 | 5/8 |
| 1-1/4 | 4 | 1/2 | 4 | 5/8 | 4 | 5/8 |
| 1-1/2 | 4 | 1/2 | 4 | 3/4 | 4 | 3/4 |
| 2 | 4 | 5/8 | 8 | 5/8 | 8 | 5/8 |
| 2-1/2 | 4 | 5/8 | 8 | 3/4 | 8 | 3/4 |
| 3 | 4 | 5/8 | 8 | 3/4 | 8 | 3/4 |
| 3-1/2 | 8 | 5/8 | 8 | 3/4 | 8 | 3/4 |
| 4 | 8 | 5/8 | 8 | 3/4 | 8 | 7/8 |
| 5 | 8 | 3/4 | 8 | 3/4 | 8 | 1 |
| 6 | 8 | 3/4 | 12 | 3/4 | 12 | 1 |
| 8 | 8 | 3/4 | 12 | 7/8 | 12 | 1-1/8 |
| 10 | 12 | 7/8 | 16 | 1 | 16 | 1-1/4 |
| 12 | 12 | 7/8 | 16 | 1-1/8 | 20 | 1-1/4 |
| 14 | 12 | 1 | 20 | 1-1/8 | 20 | 1-3/8 |
| 16 | 16 | 1 | 20 | 1-1/4 | 20 | 1-1/2 |
| 18 | 16 | 1-1/8 | 24 | 1-1/4 | 20 | 1-5/8 |
| 20 | 20 | 1-1/8 | 24 | 1-1/4 | 24 | 1-5/8 |
| 24 | 20 | 1-1/4 | 24 | 1-1/2 | 24 | 1-7/8 |
