ASME B16.47 Series B Class 300 Flange Dimensions (NPS 26 to NPS 60)

Reference manual hosted for technician access. 1 pages.

Brand

ASME B16.47 Series B

Equipment

Class 300 compact large-diameter weld-neck flange

Document type

Dimensional reference

Revision

ASME B16.47

Issued

2026-06-16

Pages

Format

PDF (application/pdf)

ASME B16.47 Series B Class 300 large-diameter flange dimensions: flange outside diameter, bolt-circle diameter, number of bolts, bolt-hole size and stud size for weld-neck flanges from NPS 26 through NPS 60 — the higher-pressure companion to Series B Class 150 and the compact alternative to Series A. Includes NPS 30 (920.8 mm bolt circle, 36 studs), NPS 36 (1089.0 mm, 32 studs) and NPS 48 (1416.0 mm, 40 studs). Series B is NOT interchangeable with Series A, and neither mates to an ASME B16.5 flange. Values cross-checked across three independent reference tables (mm and inch), which agree on outside diameter, bolt circle and bolt count for every NPS.

ASME B16.47 Series B Class 300 flange dimensions (NPS 26 to NPS 60)

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 that carries more, smaller bolts on a smaller bolt circle, formerly API 605). 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 300 is the higher-pressure companion to Class 150: a larger bolt circle, larger studs and a thicker flange for the same NPS. The values below are the Series B Class 300 dimensions for the weld-neck flange, cross-checked across three independent reference tables.

NPS	Flange OD (mm)	Bolt circle (mm)	No. of bolts	Bolt hole (mm)	Stud size
NPS 26	865	803.3	32	34.9	1 1/4 in
NPS 28	920	857.2	36	34.9	1 1/4 in
NPS 30	990	920.8	36	38.1	1 3/8 in
NPS 32	1055	977.9	32	41.3	1 1/2 in
NPS 34	1110	1031.9	36	41.3	1 1/2 in
NPS 36	1170	1089.0	32	44.5	1 5/8 in
NPS 38	1220	1139.8	36	44.5	1 5/8 in
NPS 40	1275	1190.6	40	44.5	1 5/8 in
NPS 42	1335	1244.6	36	47.6	1 3/4 in
NPS 44	1385	1295.4	40	47.6	1 3/4 in
NPS 46	1460	1365.2	36	50.8	1 7/8 in
NPS 48	1510	1416.0	40	50.8	1 7/8 in
NPS 50	1560	1466.8	44	50.8	1 7/8 in
NPS 52	1615	1517.6	48	50.8	1 7/8 in
NPS 54	1675	1578.0	48	50.8	1 7/8 in
NPS 56	1765	1651.0	36	60.3	2 1/4 in
NPS 58	1825	1712.9	40	60.3	2 1/4 in
NPS 60	1880	1763.7	40	60.3	2 1/4 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 34.9 mm (1 3/8 in) hole takes a 1 1/4 in stud, the 44.5 mm (1 3/4 in) hole a 1 5/8 in stud and the 60.3 mm (2 3/8 in) hole a 2 1/4 in stud. The bolt count in Series B Class 300 does not rise steadily with NPS — it steps up and down as the stud size changes — so confirm the exact count for the specific NPS rather than interpolating. The three tables agree exactly on the outside diameter, bolt circle and bolt count for every NPS.

Reading the dimensions

Flange OD — the overall diameter of the flange disc; sets the space the flange occupies. Series B is smaller in outside diameter than Series A at the same NPS and rating.
Bolt circle — the diameter of the circle through the bolt-hole centres, also called the PCD. This is the figure to lay out or check the drilling against and the single most important number for matching a mating flange.
Number of bolts — equally spaced; both mating flanges share the same count. Series B Class 300 carries 32 to 48 studs across the range, and the count is not monotonic with NPS.
Bolt hole — the drilled hole diameter; the clearance over the stud lets two flanges line up.
Stud size — the diameter of the stud bolt (these flanges are bolted with stud bolts and two nuts, not through-bolts). Use the full set; do not part-populate a flange.

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 B Class 300 table or the flange maker’s data sheet.

Selecting and matching

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 B flange will not mate to a Series A flange of the same NPS and rating — the outside diameter, bolt circle and bolt count all differ — and neither mates to an ASME B16.5 flange. Series B saves weight and bolt-up effort and suits a line and mating equipment built to Series B throughout; Series A is the choice where a Series A flange is already installed or the heavier flange suits the duty. The rating (Class 300 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 B Class 300 share the same outside diameter, bolt circle, bolt hole, bolt count and stud size.

Dimensions are nominal ASME B16.47 Series B 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.

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Reference compiled for identification and cross-reference. Dimensions are nominal; confirm against the controlling ASME B16.47 Series B ASME B16.47 revision and the specific component data sheets before manufacture or procurement. All trademarks are the property of their respective owners.