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- NACE MR0175/ISO 15156-2
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ASME B18.31.2 Clamping Type Full Body Studs – Dimensions, Specifications & Standards
Clamping Full Body Studs for High-Pressure Flange Bolting.
ASME B18.31.2 Clamping Type Full Body Studs are inch-series threaded fasteners with threads on both ends and a full-diameter unthreaded body, engineered for consistent clamping load distribution in high-pressure flange assemblies, heat exchangers, pressure vessels, and critical pipe flange joints governed by ASME B16.5 and ASME B31.3. The standard defines body diameter, overall stud length, thread length on both ends, thread pitch (UNC, UNF, or 8UN), and length tolerances. These studs comply with ASTM A1014/A1014M for UNS N07718 (Inconel 718) bolting with up to 150 ksi minimum tensile strength, superior corrosion resistance, and long service life in sour gas and subsea environments. The inch-series counterpart to B18.31.1M metric clamping studs, also commonly specified per ASTM A193 Grade B7 or B8, paired with nuts per ASTM A194. The full-body design prevents uneven stretching under bolt load, making it preferred for safety-critical gasketed joints.
ASME B18.31.2 Dimensions for Clamping Type Full Body Studs (mm)
| 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 |
ASME B18.31.2 Clamping Type Full Body Stud Length Tolerances (mm)
| 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 |
ASME B18.31.2 Dimensions for Clamping Type Full Body Studs (Inch)
| 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 |
ASME B18.31.2 Clamping Type Full Body Stud Length Tolerances (Inch)
| 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 |
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