This photo will give you a side-by-side view of the CD 728 (Right) and the CD 731.2 threadless on the left [id=79620423]. For the most part, the CD 731.2 looks identical to the CD 728; however, it has a more concave lower skirt. This was the first time that I took a good close look at the two of them together. I would speculate that the CD 731.2 might have been the earlier mould style and the later style (CD 728) was created by filling in the lower skirt. What do you think?