AFB0948L vs AFB0948L-B

What is the difference between these two Delta fans?
AFB0948L and AFB0948L-B
The specifications are the same, only the fan’s frame type differs:
               Flange type vs. Rib type.
AFB0948L is flange type frame. AFB0948L Spec
Flange Type Frame

While AFB0948L-B is a rib type frame. AFB0948L-B Spec
Rib Type Frame

Frame Type
The part numbering, including the frame type suffix, is explained in Delta’s
part number breakdown in the Application Notes on their website.