British Standard BS 4504 : Section 3.1 : 1989 - Circular Flanges for Pipes, Valves and
Fittings (PN Designated), Specification for Steel Flanges. This covers flanges in nominal
pressure ranges PN 2.5 to PN 40 and nominal sizes up to DN 4000 (see table below).
BS 4504 substantially agrees with ISO 7005-1 : 1992 (E) Part 1 : Steel Flanges.
BS 4504 : 1969 is still commonly used. This older standard allows for manufacture from
bar, whereas the latest standard specifies that forging or plate are to be used, which can
be significantly more expensive. There are minor differences in dimensions between the
two versions. The following tables are based on the later version.
