Inch-Series Full-Diameter Clamping Studs for High-Integrity Flange and Pressure Vessel Bolted Assemblies.
ASME B18.31.2 Clamping Type Full Body Studs are inch-series unheaded threaded fasteners featuring a continuous full-diameter unthreaded shank between threaded ends, engineered to provide predictable and uniform clamping load distribution in high-pressure pipe flange joints, heat exchangers, pressure vessels, and other critical bolted assemblies governed by ASME B16.5 and ASME PCC-1 gasketed joint standards. The standard defines all key dimensional parameters including body diameter, overall stud length, thread length on each end, thread pitch series, UNC, UNF, or 8UN, and all associated tolerances to ensure dimensional consistency and interchangeability across global supply chains. In demanding corrosion-resistant service environments, these studs are manufactured to ASTM A1082, the specification for high-strength stainless steel bolting material, delivering excellent resistance to chloride stress corrosion cracking, pitting corrosion, and crevice attack in offshore, marine, chemical, and food processing plant applications. The full-body design ensures that the stress cross-section is maintained at the full bolt diameter, minimizing stress concentration and improving fatigue performance under cyclic loading conditions typical in pressure piping systems. Always pair ASME B18.31.2 dimensional requirements with ASTM A1082 material specification for a complete and traceable engineering definition of full-body clamping stud bolts.
| Nominal Size |
Diameter, D | Nut End Minimum Full Thread Length, Bmin |
Minimum Body Diameter, DS | ||||
|---|---|---|---|---|---|---|---|
| L ≤ 254 mm (10 in) |
254 < L ≤ 406.4 mm (10 < L ≤ 16 in) |
L > 406.4 mm (16 in) |
UNC and NC-5 HF Threads |
UNF Threads |
8UN Threads |
||
| ¼ | 6.350 | 19.050 | 25.400 | 38.100 | 6.121 | 6.172 | … |
| 5/16 | 7.938 | 22.225 | 28.575 | 41.275 | 7.696 | 7.722 | … |
| 3/8 | 9.525 | 25.400 | 31.750 | 44.450 | 9.246 | 9.322 | … |
| 7/16 | 11.113 | 28.575 | 34.925 | 47.625 | 10.820 | 10.871 | … |
| ½ | 12.700 | 31.750 | 38.100 | 50.800 | 12.395 | 12.471 | … |
| 9/16 | 14.288 | 34.925 | 41.275 | 53.975 | 13.970 | 14.021 | … |
| 5/8 | 15.875 | 38.100 | 44.450 | 57.150 | 15.519 | 15.621 | … |
| ¾ | 19.050 | 44.450 | 50.800 | 63.500 | 18.669 | 18.771 | … |
| 7/8 | 22.225 | 50.800 | 57.150 | 69.850 | 21.819 | 21.920 | … |
| 1 | 25.400 | 57.150 | 63.500 | 76.200 | 24.968 | 25.070 | … |
| 1⅛ | 28.575 | 63.500 | 69.850 | 82.550 | 28.092 | 28.245 | 28.143 |
| 1¼ | 31.750 | 69.850 | 76.200 | 88.900 | 31.267 | 31.420 | 31.318 |
| 1⅜ | 34.925 | 76.200 | 82.550 | 95.250 | 34.392 | 34.595 | 34.493 |
| 1½ | 38.100 | 82.550 | 88.900 | 101.600 | 37.567 | 37.770 | 37.668 |
| 1⅝ | 41.275 | 88.900 | 95.250 | 107.950 | … | … | 40.843 |
| 1¾ | 44.450 | 95.250 | 101.600 | 114.300 | 43.866 | … | 44.018 |
| 1⅞ | 47.625 | 101.600 | 107.950 | 120.650 | … | … | 47.193 |
| 2 | 50.800 | 107.950 | 114.300 | 127.000 | 50.165 | … | 50.368 |
| 2¼ | 57.150 | 120.650 | 127.000 | 139.700 | 56.515 | … | 56.718 |
| 2½ | 63.500 | 133.350 | 139.700 | 152.400 | 62.814 | … | 63.068 |
| 2¾ | 69.850 | 146.050 | 152.400 | 165.100 | 69.164 | … | 69.418 |
| 3 | 76.200 | ... | 165.100 | 177.800 | 75.514 | … | 75.743 |
| 3¼ | 82.550 | ... | 177.800 | 190.500 | 81.864 | … | 82.093 |
| 3½ | 88.900 | ... | 190.500 | 203.200 | 88.214 | … | 88.443 |
| 3¾ | 95.250 | ... | 203.200 | 215.900 | 94.564 | … | 94.793 |
| 4 | 101.600 | ... | 215.900 | 228.600 | 100.914 | … | 101.143 |
| Range, LT | Tolerance |
|---|---|
| From 19.05 through 63.5 | ±1.016 |
| Over 63.5 through 101.6 | ±2.032 |
| Over 101.6 through 203.2 | ±2.540 |
| Over 203.2 through 406.4 | ±3.048 |
| Over 406.4 | ±4.572 |
| Nominal Size |
Diameter, D |
Nut End Minimum Full Thread Length, Bmin |
Minimum Body Diameter, DS | ||||
|---|---|---|---|---|---|---|---|
| L ≤ 10 | 10 < L ≤ 16 | L > 16 | UNC and NC-5 HF Threads |
UNF Threads |
8UN Threads |
||
| ¼ | 0.2500 | 0.750 | 1.000 | 1.500 | 0.241 | 0.243 | … |
| 5/16 | 0.3125 | 0.875 | 1.125 | 1.625 | 0.303 | 0.304 | … |
| 3/8 | 0.3750 | 1.000 | 1.250 | 1.750 | 0.364 | 0.367 | … |
| 7/16 | 0.4375 | 1.125 | 1.375 | 1.875 | 0.426 | 0.428 | … |
| ½ | 0.5000 | 1.250 | 1.500 | 2.000 | 0.488 | 0.491 | … |
| 9/16 | 0.5625 | 1.375 | 1.625 | 2.125 | 0.550 | 0.552 | … |
| 5/8 | 0.6250 | 1.500 | 1.750 | 2.250 | 0.611 | 0.615 | … |
| ¾ | 0.7500 | 1.750 | 2.000 | 2.500 | 0.735 | 0.739 | … |
| 7/8 | 0.8750 | 2.000 | 2.250 | 2.750 | 0.859 | 0.863 | … |
| 1 | 1.0000 | 2.250 | 2.500 | 3.000 | 0.983 | 0.987 | … |
| 1⅛ | 1.1250 | 2.500 | 2.750 | 3.250 | 1.106 | 1.112 | 1.108 |
| 1¼ | 1.2500 | 2.750 | 3.000 | 3.500 | 1.231 | 1.237 | 1.233 |
| 1⅜ | 1.3750 | 3.000 | 3.250 | 3.750 | 1.354 | 1.362 | 1.358 |
| 1½ | 1.5000 | 3.250 | 3.500 | 4.000 | 1.479 | 1.487 | 1.483 |
| 1⅝ | 1.6250 | 3.500 | 3.750 | 4.250 | … | … | 1.608 |
| 1¾ | 1.7500 | 3.750 | 4.000 | 4.500 | 1.727 | … | 1.733 |
| 1⅞ | 1.8750 | 4.000 | 4.250 | 4.750 | … | … | 1.858 |
| 2 | 2.0000 | 4.250 | 4.500 | 5.000 | 1.975 | … | 1.983 |
| 2¼ | 2.2500 | 4.750 | 5.000 | 5.500 | 2.225 | … | 2.233 |
| 2½ | 2.5000 | 5.250 | 5.500 | 6.000 | 2.473 | … | 2.483 |
| 2¾ | 2.7500 | 5.750 | 6.000 | 6.500 | 2.723 | … | 2.733 |
| 3 | 3.0000 | ... | 6.500 | 7.000 | 2.973 | … | 2.982 |
| 3¼ | 3.2500 | ... | 7.000 | 7.500 | 3.223 | … | 3.232 |
| 3½ | 3.5000 | ... | 7.500 | 8.000 | 3.473 | … | 3.482 |
| 3¾ | 3.7500 | ... | 8.000 | 8.500 | 3.723 | … | 3.732 |
| 4 | 4.0000 | ... | 8.500 | 9.000 | 3.973 | … | 3.982 |
| Range, LT | Tolerance |
|---|---|
| From ¾ through 2½ | ±0.04 |
| Over 2½ through 4 | ±0.08 |
| Over 4 through 8 | ±0.10 |
| Over 8 through 16 | ±0.12 |
| Over 16 | ±0.18 |
ASTM A1082/A1082M (2016) Table 1 lists 14 duplex (ferritic-austenitic) grades, S31100, S31260, S31803, S32101, S32202, S32205 (2205), S32304 (2304), S32506, S32550 (255), S32750 (2507), S32760, S32906, S32950 and S39277, and 5 precipitation-hardening grades, S15700 (Type 632), S17400 (Type 630), S17600 (Type 635), S17700 (Type 631) and S35500 (Type 634). Grade selection depends on design, service conditions and the mechanical properties required.
Dimensions follow ASME B18.31.2, tabulated on this page. ASTM A1082/A1082M sets chemistry (Table 1), heat treatment and mechanical properties (Tables 2 to 4) and marking (Table 5). ASTM A962/A962M general requirements also apply, and A1082 prevails where the two conflict (clause 4.1). Inch-pound units apply unless the order specifies A1082M (clause 1.4).
ISO 15156-3 Table A.24 accepts wrought duplex stainless steel for any equipment when it is solution-annealed and liquid-quenched or rapidly cooled, has 35 % to 65 % ferrite and has had no ageing heat treatment. With 30 ≤ PREN ≤ 40 and Mo ≥ 1.5 % the limit is 232 °C (450 °F) and 10 kPa (1.5 psi) H2S partial pressure; with 40 < PREN ≤ 45 it is 232 °C (450 °F) and 20 kPa (3 psi). Table A.27 accepts wrought 17-4 PH (S17400) at 33 HRC max after a double age at 620 °C (1150 °F) or a modified double age, for named wellhead, valve and subsurface components, up to 3.4 kPa (0.5 psi) H2S and pH 4.5 or above.
The grade symbol comes from Table 5 (clause 11.1), for example 32750 for S32750 or 174H for S17400 in H1150D. With Supplementary Requirement S2 the marking goes on one end of each stud; if the area is too small, the grade symbol may go on one end and the manufacturer's identification on the other. Studs under 3/8 in. [10 mm], and 1/4 in. [6 mm] studs that need more than three symbols, are marked by agreement.
Table 4: solution annealed at 1880 to 2060 °F [1025 to 1125 °C], water quenched. Up to and including 2 in.: tensile 116 ksi [800 MPa] and yield 80 ksi [550 MPa] min. Over 2 in.: 110 ksi [760 MPa] and 75 ksi [515 MPa] min. Elongation 15 % min and hardness 33 HRC or 310 HB max for both. The marking grade symbol is 32750 (Table 5).
