Commercial cased axial fans are normally used for relatively short duct lengths, unless it is a contra-rotating type such as the TCBBx2 which can develop higher pressures. Commonly used in small kitchen applications where high pressures are not needed.
The size offered on each cased axial fan model is based on the diameter of the impeller and will match the diameter of the duct used, generally connected via a matching circular flange. (See data-sheets.)
Available in single and three phase versions and most are speed controllable.