I'm sure the poly ones I got were the same dia both ends. The originals came out in crumbs so no idea what they were like.
Edit - sorry, just seen a pic and remembered that the central hole is smaller one end. I put the smaller end at the top to 'grip' the shaft and stay at the top, although I think the original just floated on the shaft, but that might have been due to their condition.
Alan
Saab 9-5 2.3t Vector Auto Estate
'81 TR7 DHC