Views: 3 Author: Site Editor Publish Time: 2026-05-06 Origin: Site
In industrial piping systems, forged flanges are essential components for pipe connections. Among various types of American standard forged flanges, the ASME B16.5 threaded flange plays a critical role in high-pressure, small-diameter, and flammable/explosive service conditions due to its unique connection method and easy installation.
From an external perspective, the primary difference between a threaded flange and a standard flange lies in the precision-machined internal pipe threads. It features a compact, disk-like structure made of high-quality forged steel. Its most notable characteristic is the elimination of welding—simply screwing a pipe with external threads into the flange's internal bore achieves the connection.
Hazardous environments: In oil/gas fields and chemical plants where open flames are prohibited, threaded flanges eliminate fire risks from welding.
Hard-to-weld materials: Ideal for galvanized pipes or high-alloy steels where welding may cause damage.
Easy maintenance: In tight spaces or temporary lines, disassembly requires only a wrench—no cutting or grinding.
ASME B16.5 is a US standard for pipe flanges and fittings, widely used in global oil, chemical, and natural gas industries. It covers flange types, dimensions, tolerances, materials, pressure ratings, and inspection methods.
Weld Neck (WN): Butt-welded; high strength, ideal for high pressure/temperature.
Slip-On (SO): Slips over pipe; easy to install, for medium/low pressure.
Blind (BL): No center hole; seals pipe ends or vessel openings.
Socket Weld (SW): Pipe inserts into socket; for small diameter (NPS 1/2–3) high-pressure.
Threaded (TH): Threaded bore; for no-welding applications like galvanized pipes or explosive areas.
Lap Joint (LJ): Used with stub end; allows different flange/pipe materials, easy disassembly.
ASME B16.5 covers pipe sizes from 1/2″ to 24″ and seven pressure classes: 150, 300, 400, 600, 900, 1500, 2500. Higher classes mean thicker flanges and larger bolts. Flanges above 24″ fall under ASME B16.47.
ASME B16.5 strictly defines threaded flange dimensions. While wall thickness does not depend on pipe wall thickness (since no welding is needed), the thread size must follow the standard.
NPS | Class | Flange OD (mm) | Bolt Circle (mm) | Bolt Hole (mm) | No. of Bolts | Thread (NPT) |
1/2″ | 150 | 88.9 | 60.45 | 15.7 | 4 | 1/2″ NPT |
1″ | 150 | 108 | 79.4 | 15.7 | 4 | 1″ NPT |
2″ | 300 | 165 | 127.0 | 19.1 | 8 | 2″ NPT |
4″ | 150 | 229 | 190.5 | 19.1 | 8 | 4″ NPT |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 88.9 | 22.4 | 11.2 | 15.7 | 30.2 | 35.1 | 4 | 15.7 | 60.45 | 0.39 |
| 3/4 | 26.7 | 98.6 | 27.7 | 12.7 | 15.7 | 38. 10 | 42.9 | 4 | 15.7 | 69.85 | 0.56 |
| 1 | 33.4 | 108 | 34.5 | 14.2 | 17.5 | 49.3 | 50.8 | 4 | 15.7 | 79.25 | 0.78 |
| 11/4 | 42.2 | 117.3 | 43.2 | 15.7 | 20.6 | 58.7 | 63.5 | 4 | 15.7 | 88.9 | 1.03 |
| 11/2 | 48.3 | 127 | 49.5 | 17.5 | 22.4 | 65 | 73.15 | 4 | 15.7 | 98.6 | 1.32 |
| 2 | 60.3 | 152.4 | 62 | 19.1 | 25.4 | 77.7 | 91.9 | 4 | 19.1 | 120.7 | 2.06 |
| 21/2 | 73 | 177.8 | 74.7 | 22.4 | 28.4 | 90.4 | 104.6 | 4 | 19.1 | 139.7 | 3.28 |
| 3 | 88.9 | 190.5 | 90.7 | 23.9 | 30.2 | 108 | 127 | 4 | 19.1 | 152.4 | 3.85 |
| 31/2 | 101.6 | 215.9 | 103.4 | 23.9 | 31.75 | 122.2 | 139.7 | 8 | 19.1 | 177.8 | 4.81 |
| 4 | 114.3 | 228.6 | 116.1 | 23.9 | 33.3 | 134.9 | 157.2 | 8 | 19.1 | 190.5 | 5.30 |
| 5 | 141.3 | 254 | 143.8 | 23.9 | 36.6 | 163.6 | 185.7 | 8 | 22.4 | 215.9 | 6.07 |
| 6 | 168.3 | 279.4 | 170.7 | 25.4 | 39.6 | 192 | 215.9 | 8 | 22.4 | 241.3 | 7.45 |
| 8 | 219.1 | 342.9 | 221.5 | 28.4 | 44.5 | 246.1 | 269.7 | 8 | 22.4 | 298.5 | 12.1 |
| 10 | 273 | 406.4 | 276.3 | 30.2 | 49.3 | 304.8 | 323.9 | 12 | 25.4 | 362 | 16.5 |
| 12 | 323.8 | 482.6 | 327.1 | 31.75 | 55.6 | 365.3 | 381 | 12 | 25.4 | 431.8 | 26.2 |
| 14 | 355.6 | 533.4 | 359.1 | 35.1 | 57.15 | 400.1 | 412.8 | 12 | 28.4 | 476.3 | 34.6 |
| 16 | 406.4 | 596.9 | 410.5 | 36.6 | 63.5 | 457.2 | 469.9 | 16 | 28.4 | 539.8 | 44.8 |
| 18 | 457.2 | 635 | 461.8 | 39.6 | 68.3 | 505 | 533.4 | 16 | 31.75 | 577.9 | 48.9 |
| 20 | 508 | 698.5 | 513.1 | 42.9 | 73.15 | 558.8 | 584.2 | 20 | 31.75 | 635 | 61.9 |
| 24 | 609.6 | 812.8 | 616 | 47.8 | 82.6 | 663.4 | 692.2 | 20 | 35.1 | 749.3 | 86.9 |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 95.2 | 22.4 | 14.2 | 22.4 | 38.1 | 35.1 | 4 | 15.7 | 66.55 | 0.64 |
| 3/4 | 26.7 | 117.3 | 27.7 | 15.7 | 25.4 | 47.7 | 42.9 | 4 | 19.1 | 82.5 | 1. 12 |
| 1 | 33.4 | 123.9 | 34.5 | 17.5 | 26.9 | 53.8 | 50.8 | 4 | 19.1 | 88.9 | 1.36 |
| 11/4 | 42.2 | 133.3 | 43.2 | 19 | 26.9 | 63.5 | 63.5 | 4 | 19.1 | 98.6 | 1.68 |
| 11/2 | 48.3 | 155.4 | 49.5 | 20.6 | 30.2 | 69.85 | 73.15 | 4 | 22.4 | 114.3 | 2.49 |
| 2 | 60.3 | 165.1 | 62 | 22.3 | 33.2 | 84 | 91.9 | 8 | 19.1 | 127 | 2.87 |
| 21/2 | 73 | 190.5 | 74.7 | 25.4 | 38.1 | 100 | 104.6 | 8 | 22.4 | 149.4 | 4.32 |
| 3 | 88.9 | 209.5 | 90.7 | 28.4 | 42.9 | 117.3 | 127 | 8 | 22.4 | 168.1 | 5.85 |
| 31/2 | 101.6 | 228.6 | 103.4 | 30.2 | 44.4 | 133.3 | 139.7 | 8 | 22.4 | 184.2 | 7.34 |
| 4 | 114.3 | 254 | 116.1 | 31.7 | 47.7 | 146 | 157.2 | 8 | 22.4 | 200.1 | 9.61 |
| 5 | 141.3 | 279.4 | 143.8 | 35 | 50.8 | 177.8 | 185.7 | 8 | 22.4 | 234.9 | 12.3 |
| 6 | 168.3 | 317.5 | 170.7 | 36.5 | 52.3 | 206.2 | 215.9 | 12 | 22.4 | 269.7 | 15.6 |
| 8 | 219. 1 | 381 | 221.5 | 41.1 | 61.9 | 260.3 | 269.7 | 12 | 25.4 | 330.2 | 24.2 |
| 10 | 273 | 444.5 | 276.3 | 47.7 | 66.55 | 320.5 | 323.9 | 16 | 28.4 | 387.3 | 34.1 |
| 12 | 323.8 | 520.7 | 327.1 | 50.8 | 73.15 | 374.6 | 381 | 16 | 31.7 | 450.8 | 49.8 |
| 14 | 355.6 | 584.2 | 359.1 | 53.8 | 76.2 | 425.4 | 412.8 | 20 | 31.7 | 514.4 | 69.9 |
| 16 | 406.4 | 647.7 | 410.5 | 57.15 | 82.5 | 482.6 | 469.9 | 20 | 35 | 571.5 | 88.1 |
| 18 | 457.2 | 711.2 | 461.8 | 60.45 | 88.9 | 533.4 | 533.4 | 24 | 35 | 628.7 | 109 |
| 20 | 508 | 774.7 | 513.1 | 63.5 | 95.2 | 587.2 | 584.2 | 24 | 35 | 685.8 | 134 |
| 24 | 609.6 | 914.4 | 616 | 69.85 | 106.4 | 701.5 | 692.2 | 24 | 41 | 812.8 | 201 |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 95.3 | 22.4 | 14.2 | 22.4 | 38.1 | 35. 10 | 4 | 15.7 | 66.55 | 0.74 |
| 3/4 | 26.7 | 117.3 | 27.7 | 15.7 | 25.4 | 47.7 | 42.9 | 4 | 19.1 | 82.5 | 1.27 |
| 1 | 33.4 | 124 | 34.5 | 17.5 | 26.9 | 53.8 | 50.8 | 4 | 19.1 | 88.9 | 1.52 |
| 11/4 | 42.2 | 133.4 | 43.2 | 20.6 | 28.4 | 63.5 | 63.5 | 4 | 19.1 | 98.6 | 2.03 |
| 11/2 | 48.3 | 155.4 | 49.5 | 22.4 | 31.75 | 69.85 | 73. 15 | 4 | 22.4 | 114.3 | 2.96 |
| 2 | 60.3 | 165.1 | 62 | 25.4 | 36.6 | 84 | 91.9 | 8 | 19.1 | 127 | 3.62 |
| 21/2 | 73 | 190.5 | 74.7 | 28.4 | 41.1 | 100 | 104.6 | 8 | 22.4 | 149.4 | 5.28 |
| 3 | 88.9 | 209.6 | 90.7 | 31.75 | 46 | 117.3 | 127 | 8 | 22.4 | 168. 1 | 7.00 |
| 31/2 | 101.6 | 228.6 | 103.4 | 35.1 | 49.3 | 133.3 | 139.7 | 8 | 25.4 | 184.2 | 8.84 |
| 4 | 114.3 | 254 | 116.1 | 35.1 | 50.8 | 146 | 157.2 | 8 | 25.4 | 200. 1 | 11. 1 |
| 5 | 141.3 | 279.4 | 143.8 | 38.1 | 53.8 | 177.8 | 185.7 | 8 | 25.4 | 234.9 | 13.9 |
| 6 | 168.3 | 317.5 | 170.7 | 41.1 | 57.15 | 206.2 | 215.9 | 12 | 25.4 | 269.7 | 18.3 |
| 8 | 219.1 | 381 | 221.5 | 47.8 | 68.3 | 260.3 | 269.7 | 12 | 28.4 | 330.2 | 28.6 |
| 10 | 273 | 444.5 | 276.3 | 53.8 | 73.15 | 320.5 | 323.9 | 16 | 31.75 | 387.3 | 39.2 |
| 12 | 323.8 | 520.7 | 327. 1 | 57.15 | 79.25 | 374.6 | 381 | 16 | 35.1 | 450.8 | 57.0 |
| 14 | 355.6 | 584.2 | 359. 1 | 60.05 | 84.1 | 425.4 | 412.8 | 20 | 35.1 | 514.4 | 79.1 |
| 16 | 406.4 | 647.7 | 410.5 | 63.5 | 93.7 | 482.6 | 469.9 | 20 | 38.1 | 571.5 | 101 |
| 18 | 457.2 | 711.2 | 461.8 | 66.55 | 98.6 | 533.4 | 533.4 | 24 | 38.1 | 628.7 | 123 |
| 20 | 508 | 774.7 | 513. 1 | 69.85 | 101.6 | 587.2 | 584.2 | 24 | 41.1 | 685.8 | 146 |
| 24 | 609.6 | 914.4 | 616 | 76.2 | 114.3 | 701.5 | 692.2 | 24 | 47.8 | 812.8 | 219 |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 95.3 | 22.4 | 14.2 | 22.4 | 38.1 | 35.1 | 4 | 15.7 | 66.55 | 0.74 |
| 3/4 | 26.7 | 117.3 | 27.7 | 15.7 | 25.4 | 47.8 | 42.9 | 4 | 19.1 | 82.6 | 1.27 |
| 1 | 33.4 | 124 | 34.5 | 17.5 | 26.9 | 53.8 | 50.8 | 4 | 19.1 | 88.9 | 1.52 |
| 11/4 | 42.2 | 133.4 | 43.2 | 20.6 | 28.4 | 63.5 | 63.5 | 4 | 19.1 | 98.6 | 2.03 |
| 11/2 | 48.3 | 155.4 | 49.5 | 22.4 | 31.75 | 69.85 | 73.15 | 4 | 22.4 | 114.3 | 2.96 |
| 2 | 60.3 | 165.1 | 62 | 25.4 | 36.6 | 84.1 | 91.9 | 8 | 19.1 | 127 | 3.62 |
| 21/2 | 73 | 190.5 | 74.7 | 28.4 | 41.1 | 100.1 | 104.6 | 8 | 22.4 | 149.4 | 5.28 |
| 3 | 88.9 | 209.6 | 90.7 | 31.75 | 46 | 117.3 | 127 | 8 | 22.4 | 168.1 | 7.00 |
| 31/2 | 101.6 | 228.6 | 103.4 | 35.1 | 49.3 | 133.4 | 139.7 | 8 | 25.4 | 184.2 | 8.84 |
| 4 | 114.3 | 273.1 | 116.1 | 38.1 | 53.8 | 152.4 | 157.2 | 8 | 25.4 | 215.9 | 14.5 |
| 5 | 141.3 | 330.2 | 143.8 | 44.5 | 60.45 | 189 | 185.7 | 8 | 28.4 | 266.7 | 24.4 |
| 6 | 168.3 | 355.6 | 170.7 | 47.8 | 66.55 | 222.3 | 215.9 | 12 | 28.4 | 292.1 | 28.7 |
| 8 | 219. 1 | 419.1 | 221.5 | 55.6 | 76.2 | 273.1 | 269.7 | 12 | 31.75 | 349.3 | 43.4 |
| 10 | 273 | 508 | 276.3 | 63.5 | 85.9 | 342.9 | 323.9 | 16 | 35.1 | 431.8 | 70.3 |
| 12 | 323.8 | 558.8 | 327.1 | 66.55 | 91.9 | 400.1 | 381 | 20 | 35.1 | 489 | 84.2 |
| 14 | 355.6 | 603.3 | 359.1 | 69.85 | 93.7 | 431.8 | 412.8 | 20 | 38.1 | 527.1 | 98.7 |
| 16 | 406.4 | 685.8 | 410.5 | 76.2 | 106.4 | 495.3 | 469.9 | 20 | 41.1 | 603.3 | 142 |
| 18 | 457.2 | 743 | 461.8 | 82.6 | 117.3 | 546.1 | 533.4 | 20 | 44.5 | 654.1 | 173 |
| 20 | 508 | 812.8 | 513.1 | 88.9 | 127 | 609.6 | 584.2 | 24 | 44.5 | 723.9 | 220 |
| 24 | 609.6 | 939.8 | 616 | 101.6 | 139.7 | 717.6 | 692.2 | 24 | 50.8 | 838.2 | 312 |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 120.6 | 22.4 | 22.4 | 31.7 | 38. 10 | 35.1 | 4 | 22.4 | 82.5 | 1.74 |
| 3/4 | 26.7 | 130 | 27.7 | 25.4 | 35 | 44.4 | 42.9 | 4 | 22.4 | 88.9 | 2.34 |
| 1 | 33.4 | 149.3 | 34.5 | 28.4 | 41.1 | 52.3 | 50.8 | 4 | 25.4 | 101.6 | 3.44 |
| 11/4 | 42.2 | 158.7 | 43.2 | 28.4 | 41.1 | 63.5 | 63.5 | 4 | 25.4 | 111.2 | 3.91 |
| 11/2 | 48.3 | 177.8 | 49.5 | 31.7 | 44.5 | 69.85 | 73.15 | 4 | 28.4 | 123.9 | 5.36 |
| 2 | 60.3 | 215.9 | 62 | 38.1 | 57.15 | 104.6 | 91.9 | 8 | 25.4 | 165.1 | 9.85 |
| 21/2 | 73 | 244.3 | 74.7 | 41.1 | 63.5 | 123.9 | 104.6 | 8 | 28.4 | 190.5 | 13.7 |
| 3 | 88.9 | 241.3 | 90.7 | 38.1 | 53.8 | 127 | 127 | 8 | 25.4 | 190.5 | 11.6 |
| 4 | 114.3 | 292.1 | 116.1 | 44.4 | 69.85 | 158.7 | 157.2 | 8 | 31.7 | 234.9 | 19.7 |
| 5 | 141.3 | 349.2 | 143.8 | 50.8 | 79.25 | 190.5 | 185.7 | 8 | 35 | 279.4 | 31.9 |
| 6 | 168.3 | 381 | 170.7 | 55.6 | 85.8 | 234.9 | 215.9 | 12 | 31.7 | 317.5 | 41.1 |
| 8 | 219.1 | 469.9 | 221.5 | 63.5 | 101.6 | 298.4 | 269.7 | 12 | 38.1 | 393.7 | 70.7 |
| 10 | 273 | 546.1 | 276.3 | 69.85 | 107.9 | 368.3 | 323.9 | 16 | 38.1 | 469.9 | 101 |
| 12 | 323.8 | 609.6 | 327.1 | 79.25 | 117.3 | 419.1 | 381 | 20 | 38.1 | 533.4 | 133 |
| 14 | 355.6 | 641.3 | 359.1 | 85.8 | 130 | 450.8 | 412.8 | 20 | 41.1 | 558.8 | 153 |
| 16 | 406.4 | 704.8 | 410.5 | 88.9 | 133.3 | 508 | 469.9 | 20 | 44.4 | 615.9 | 185 |
| 18 | 457.2 | 787.4 | 461.8 | 101.6 | 152.4 | 565.1 | 533.4 | 20 | 50.8 | 685.8 | 258 |
| 20 | 508 | 857.2 | 513.1 | 107.9 | 158.7 | 622.3 | 584.2 | 20 | 53.8 | 749.3 | 317 |
| 24 | 609.6 | 1041.4 | 616 | 139.7 | 203.2 | 749.3 | 692.2 | 20 | 66.55 | 901.7 | 606 |
| Nominal Pipe Size | A | B | C | D | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.3 | 120.6 | 22.4 | 22.4 | 31.7 | 38.1 | 35.1 | 4 | 22.4 | 82.5 | 1.74 |
| 3/4 | 26.7 | 130 | 27.7 | 25.4 | 35 | 44.4 | 42.9 | 4 | 22.4 | 88.9 | 2.34 |
| 1 | 33.4 | 149.3 | 34.5 | 28.4 | 41.1 | 52.3 | 50.8 | 4 | 25.4 | 101.6 | 3.44 |
| 11/4 | 42.2 | 158.7 | 43.2 | 28.4 | 41.1 | 63.5 | 63.5 | 4 | 25.4 | 111.2 | 3.91 |
| 11/2 | 48.3 | 177.8 | 49.5 | 31.7 | 44.5 | 69.85 | 73.15 | 4 | 28.4 | 123.9 | 5.36 |
| 2 | 60.3 | 215.9 | 62 | 38.1 | 57.15 | 104.6 | 91.9 | 8 | 25.4 | 165.1 | 9.85 |
| 21/2 | 73 | 244.3 | 74.7 | 41.1 | 63.5 | 123.9 | 104.6 | 8 | 28.4 | 190.5 | 13.7 |
NPT (National Pipe Thread): Tapered design, self-sealing. Used mainly in US/Canada.
BSPP (British Standard Parallel Pipe): Parallel threads, 55° angle, requires gaskets or sealant. Used in Europe/Australia.
ASME B16.5 uses NPT threads. However, threaded flanges are not recommended for extreme temperature fluctuations (above 260°C or below -45°C) due to potential leakage.
Threaded: Mechanical, no welding.
Socket Weld: Welded with fillet weld.
Threaded: No open flame allowed (e.g., offshore platforms, galvanized pipes).
Socket Weld: General high-pressure systems where welding is permitted.
Threaded: Faster installation, no NDT or welder qualification needed.
Socket Weld: Slower, requires welding and NDT.
Choose threaded flanges where welding is prohibited or materials are hard to weld. Choose socket weld flanges for permanent, high-temperature, high-pressure systems requiring better fatigue and leak resistance.
ASME B16.5 flanges are widely used in:
Oil & gas: Pipelines, wellhead devices, instrument taps.
Chemical & power: Connecting valves, pumps, reactors.
Fire protection & water systems: Indoor fire piping, galvanized pipe connections.
The ASME B16.5 threaded flange plays a unique and critical role in industrial piping due to its weld-free design and suitability for hazardous environments. Standardized dimensions ensure global interchangeability and safe operation. Always select flanges based on pressure, temperature, and site safety requirements, and strictly follow the ASME B16.5 pressure-temperature ratings.
