Apart from the functional design of a flange, flange dimensions are the most likely factor to impact flange choices when designing, maintaining, or updating a piping system.
However, you must consider how the flange interfaces with the pipe and the gaskets in use to ensure proper sizing.
Common considerations include:
Outside diameter: The distance between two opposing edges of the flange face
Thickness: A measure of the thickness of the outer attaching rim
Bolt circle diameter: The distance between opposing bolt holes when measured from centre to centre
Pipe size: A designation of the pipe size with which the flange corresponds
Nominal bore size: A measurement of the flange connectors inner diameter
