Their is no diff in shaft size on them blower wheels. The dif is the diameter and the size of the blades themselves. Some models carry a wing that is attached to the front of the assembly to act as a helper in aerodynamics I guess. Others do not have this wing attached to the front of the blower assembly. If this was an attempt to divert heat from the hub it was not very successful. LOL I have found that the cheapest offering of these wheels will work if the said diverter is omitted.