Flange Dimensions Reference

What a Dimension Table Contains

Every standardized flange table presents the same family of dimensions, even when the standard itself is written for a different pressure regime. Outside diameter sets the physical footprint of the flange and determines whether the part will clear adjacent piping, supports, and equipment nozzles. Bolt circle diameter dictates where the studs land relative to that outside diameter and is the single most common interchange criterion when an engineer is checking whether an AWWA C207 Class D flange will bolt up to an ANSI B16.1 Class 125 mating part.

Bolt count and bolt hole diameter combine with bolt circle to define the bolting pattern. The bolt holes are straddle drilled, meaning they sit symmetrically across the principal horizontal and vertical centerlines of the flange face. Hub dimensions cover length through hub, hub diameter at the base, hub diameter at the point of welding, and the small end bore that matches the pipe schedule the flange will be welded to. Raised face dimensions add face height above the back of the flange and face diameter, both of which the gasket selection depends on directly.

For ring joint flanges the raised face is replaced by an octagonal or oval groove machined into the face. The groove number, groove mean diameter, groove width, and groove depth all come straight from the API or ASME tables and must match the ring gasket geometry on both sides of the joint.

AWWA C207 Waterworks Dimensions

AWWA C207 covers steel flanges for waterworks service and is written for the lighter pressures typical of municipal water distribution and treatment. The Class B, D, E, and F families top out around 86, 175, 275, and 300 PSI cold working pressure respectively. The dimensional importance is that Class D shares its outside diameter, bolt circle, bolt count, and bolt hole size with ANSI B16.1 Class 125 cast iron and with the ANSI B16.5 Class 150 pattern in most sizes. That dimensional compatibility is why an AWWA flanged butterfly valve can be bolted to a Class 150 steel pipe flange in the field.

What does not transfer is the working pressure. A Class B flange at 86 PSI looks identical to a Class 125 cast iron flange from the bolt side, but it is not rated for the same service. Always confirm the class stamping and the project specification before assuming interchangeability.

Specification Gotchas

Class 600 and higher raised face flanges have a 1/4 inch raised face by default. Class 150 and 300 have a 1/16 inch raised face. When that detail is missed, the bolt length and gasket compression calculations both come out wrong. Check the standard or our dimension calculator before ordering studs.

ASME B16.47 Series A and Series B cover large diameter flanges from NPS 26 through NPS 60 but use different dimensional patterns. Series A is the heavier MSS SP-44 derived pattern. Series B is lighter and comes from API 605. The two are not interchangeable in either bolt pattern or outside diameter. The bid document must call out the series.

Lightweight Class 125LW flanges intended for valve bodies and pump casings share the bolt pattern with Class 150 but are dimensionally lighter through the hub and face. They are not rated for the same piping service and should not be substituted without engineering review.