This International Standard specifies size designations for industrial fans and specifies dimensions for the cir-cular and rectangular flanges of general purpose in-dustrial fans as defined in 3.1.1. It does not apply to cross-flow fans, or fan appliances used for household or similar applications.
For circular flanges, this International Standard pro-vides two different flange series, one for standard casing thicknesses and a second for heavy duty fans as used on board sea-going vessels or in heavy indus-try.
In order not to restrict fan designs unduly, only the pitch diameter, hole numbers and hole diameters are standardized. Flange thickness as well as internal and external flange diameters can be chosen freely within the limits of good engineering practice.