Thanks for the reply Brian. It's not surprising that the same model pump would have variations. The largest difference is more than I might expect. My glass faces are flush with the opening in the sheet metal.Your photo does give me some idea on how I might have to modify mine if I end up having to cut the knob off. There is almost 3/8" of shaft the extends out beyond the glass and I could thread it, if necessary, to accept a different knob.