Fred, thanks for the reply. My fan (original I think) has round heads on both sides but the configuration of the blades (offsets of the blades) only allow it to mount one way. The sales person I talked to about it was not real helpful. She did measure the diameter of another pump and it was the same as she sent me. Her suggestion was to change the pulley. I subsequently talked to Chevs of the 40's and they had a pump with a diameter hub that I think will fit my fan---so I order it. Will return the one to JC if that is the case.