What is DN?

Put simply, it is a rough translation of mm from imperial sizes, assuming that an inch is 25mm.

We refer to a 12" flange as DN300, when in fact it is 304mm.

What is the PCD?

The PCD of a flange is one of the critical dimensions.

PCD (Pitch Circle Diameter) is the diameter of a circle that goes through each of the bolt holes.

British Standard - BS10

Table D

Table E

Table F

Table G

Table H

Table J

Table K

Table E is the most popular for applications with water.

All dimensions are specified in inches.

Australian Standard - AS2129

Table C

Table D

Table E

Table F

Table G

Table H

Table J

These flanges are equivalent to the BS10 flanges, except that all dimensions are specified in mm.

In some sizes, bolt holes are slightly larger to give better clearance.

American National Standards Institute (ANSI)

ANSI 125

ANSI 150

ANSI 300

ANSI 600

ANSI 900

 ANSI 1500

Higher numbers denote higher pressures.

Sometimes people use the word 'Class' instead of ANSI. e.g. an ANSI 150 flange might be called a 'Class 150'

All dimensions are specified in inches.

British Standard

BS4504

BS4504-6

  BS4504-10

  BS4504-16

  BS4504-25

  BS4504-40

BS4504-64

 BS4504-100

PN6

PN10

PN16

PN25

PN40

PN64

 PN100

Engineers use the prefix PN (Pressure Nominale). e.g. a BA4504-16 flange will commonly be referred to as a PN16

Generally, a PN16 flange is designed to withstand pressures up to 16 bar.

All dimensions are specified in mm.

*AS2129 still in use but now only covers Table D to H (Table C now obsolete, Table J to T now replaced by AS4331 which is a replication of ISO7500-1 which in turn is equivalent to ASME 150-2500 class ANSI B16.5). AS4087 is the new standard covering Table D to H. The same drilling is specified but the PN rating system is used (PN16 to PN35).

** British metric standard BS4504 is now obsolete and replaced by EN1092-1 edition 09-2008 for steel flanges which also incorporates DIN standard. Flange drillings in EN1092-1 are generally the same as BS4504 but EN1092-1 covers a wider range. This includes EN1092-1 and BS4054 tables. For EN1092-1 table click here