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ASME B16.5 flange bolt chart

Pipe size and pressure class in, stud quantity, diameter and length out. Every class has its own page, filterable by NPS, copyable as CSV and laid out to print cleanly on A4.

Bolted flange joint in service
Bolted pipe flanges and a gate valve in a process plant

Class 150

19.6 bar

The most common class in any plant. Low pressure, small studs, and the one where a wrong bolt length is most likely to go unnoticed until the joint leaks.

NPS ½" – 24" · 20 rows

Class 300

51.1 bar

Twice the pressure of Class 150 and noticeably more bolts. Note that NPS 2 jumps from four studs to eight — a detail that catches people re-bolting from a Class 150 drawing.

NPS ½" – 24" · 20 rows

Class 600

102.1 bar

Where studs start getting long enough that thread engagement and nut runout matter. Class 400 flanges up to NPS 3 use this same bolting.

NPS ½" – 24" · 19 rows

Class 900

153.2 bar

From NPS ½ to 2½ the Class 900 flange is dimensionally identical to Class 1500 — use the Class 1500 rows for those sizes.

NPS 3" – 24" · 12 rows

Class 1500

255.3 bar

Studs here reach 3½ in diameter and 20 in length. At this size the joint is normally tensioned hydraulically rather than torqued, and stud straightness and thread quality stop being cosmetic.

NPS ½" – 24" · 19 rows

Class 2500

425.5 bar

The highest class in B16.5, and it stops at NPS 12. Above that the flange becomes a special or moves to a compact connector.

NPS ½" – 12" · 14 rows

What the chart does not cover

  • RTJ flanges. The extra length depends on the ring groove and the ring type, so we confirm it per job rather than publishing a number that could be wrong.
  • Class 400. Up to NPS 3 it shares Class 600 bolting; above that, send us the flange detail.
  • ASME B16.47 large diameter flanges, NPS 26 and above. We manufacture for both Series A and Series B — ask and we will work the size from your flange drawing.

Series A or Series B?

ASME B16.47 covers flanges from NPS 26 to 60 in two incompatible families. Series A, from MSS SP-44, is heavier with a larger bolt circle and fewer, larger studs. Series B, from API 605, is more compact with more studs of smaller diameter. They do not bolt to each other, and a Series A stud will not fit a Series B flange, so the series has to be on the enquiry.

Need a quotation?

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