Round Connections
Minimum air-tightness classes C (DIN EN 12237) and ATC3 (DIN EN 16798-3).
Unless indicated otherwise, the diameters always correspond to the inner diameters of the ducts.
What differentiates the AF, LF, BF and UF flanges is the way they are fixed into the circular ducts. They can still be combined with each other (connecting an AF flange with an LF flange for example) as they have all been designed to be assembled together with SR joining clips.
