Series 6 fans are those deep-dished back plate, i.e. Dimension “E” is relatively large. This type is used on many European motors and some older American designs. To change European frame sizes (IEC numbers) to the approximate NEMA frame, multiply the IEC number by (1.6). The IEC frame number is the motor shaft height (D) in millimeters. The deep hub recess allows the fan to fit around a protruding bearing housing. Some of the Series 1 fans also have a sizeable hub recess, so that the distinction between them and the Series 6 is not rigorous.
Select the Overall Diameter Range (D) that the fan you are looking for fits into.