ASME B16.47 Series A Class 900 large-diameter flange dimensions: flange outside diameter O, bolt-circle diameter, number of bolts, bolt-hole size and stud size for weld-neck flanges from NPS 26 through NPS 48 — the highest-pressure Series A class, which is tabulated to NPS 48. Includes NPS 30 (1085.8 mm bolt circle, 20 studs), NPS 36 (1289.0 mm, 20 studs) and NPS 48 (1587.5 mm, 24 studs). For Class 400/600/900 the Series A flange adopts the Series B outside diameter and bolt circle at NPS 38 and larger, so NPS 38 shares the NPS 36 outside diameter and bolt circle. Series A is not interchangeable with Series B, and Class 900 is not interchangeable with Class 150, 300 or 600. Values cross-checked across three independent reference tables.
ASME B16.47 covers steel pipe flanges from NPS 26 to NPS 60, the range above the NPS 24 ceiling of ASME B16.5. It defines two non-interchangeable series: Series A (the larger, more robust flange, formerly MSS SP-44) and Series B (a more compact flange with more, smaller bolts). The two series share neither the outside diameter nor the bolt pattern at a given NPS and rating, so the series must be confirmed before a flange is ordered or matched. Class 900 is the highest-pressure Series A class and is tabulated from NPS 26 to NPS 48. The values below are the Series A Class 900 dimensions for the weld-neck flange, cross-checked across three independent reference tables.
| NPS | Flange OD O (mm) | Bolt circle (mm) | No. of bolts | Bolt hole (mm) | Stud size |
|---|---|---|---|---|---|
| NPS 26 | 1085.9 | 952.5 | 20 | 73.0 | 2 3/4 in |
| NPS 28 | 1168.4 | 1022.4 | 20 | 79.4 | 3 in |
| NPS 30 | 1231.9 | 1085.8 | 20 | 79.4 | 3 in |
| NPS 32 | 1314.5 | 1155.7 | 20 | 85.7 | 3 1/4 in |
| NPS 34 | 1397.0 | 1225.6 | 20 | 92.1 | 3 1/2 in |
| NPS 36 | 1460.5 | 1289.0 | 20 | 92.1 | 3 1/2 in |
| NPS 38 | 1460.5 | 1289.0 | 20 | 92.1 | 3 1/2 in |
| NPS 40 | 1511.3 | 1339.8 | 24 | 92.1 | 3 1/2 in |
| NPS 42 | 1562.1 | 1390.6 | 24 | 92.1 | 3 1/2 in |
| NPS 44 | 1647.8 | 1463.7 | 24 | 98.4 | 3 3/4 in |
| NPS 46 | 1733.6 | 1536.7 | 24 | 104.8 | 4 in |
| NPS 48 | 1784.4 | 1587.5 | 24 | 104.8 | 4 in |
Bolt holes are drilled on the bolt circle, straddling the centreline and equally spaced. ASME B16.47 drills the hole 1/8 in larger than the stud, so the 73.0 mm (2 7/8 in) hole takes a 2 3/4 in stud, the 92.1 mm (3 5/8 in) hole a 3 1/2 in stud and the 104.8 mm (4 1/8 in) hole a 4 in stud. For Class 400, 600 and 900 the Series A flange adopts the Series B outside diameter and bolt circle at NPS 38 and larger, so NPS 38 shares the NPS 36 outside diameter (1460.5 mm) and bolt circle (1289.0 mm) — a genuine feature of the standard, confirmed across the reference tables, not a typographical error. Bolt circle, bolt count, bolt-hole and stud size agree across all three reference tables for every NPS; the outside diameter agrees across the three inch tables, with the single NPS 28 outlier resolved two-to-one to 46.00 in (1168.4 mm).
Flange thickness and hub dimensions are not tabled here: they vary with the flange type (weld-neck, blind, slip-on) and the published columns differ between reference tables. Take the thickness for a given NPS from the controlling ASME B16.47 Series A table or the flange maker’s data sheet.
Two flanges bolt together only when the standard, series, NPS, rating and bolt pattern all agree, so confirm all five before ordering. A B16.47 Series A flange will not mate to a Series B flange of the same NPS and rating — the outside diameter, bolt circle and bolt count differ — and neither mates to an ASME B16.5 flange. Class 900 carries a larger bolt circle and bigger studs than Class 150, 300 or 600 at the same NPS, so the ratings are not interchangeable. Series A is the common choice where a Series A flange is already installed or where the heavier flange suits the duty; Series B saves weight and bolt-up effort where the line and the mating equipment are built to Series B throughout. The rating (Class 900 here) sets the bolt circle and the facing; the bore, hub and thickness then follow the flange type. The dimensions above are for the weld-neck flange; blind flanges to B16.47 Series A Class 900 share the same outside diameter, bolt circle, bolt hole, bolt count and stud size.
Dimensions are nominal ASME B16.47 Series A values and provided for identification and cross-reference. Confirm against the controlling standard and the specific flange maker’s current data sheet before manufacture or procurement.