Part # 90-423-1419
Alternate Part #'s O-419, 90-423-5450, APCO2252, FCHFCAO419
Your Source for Swimming Pool & Spa Parts - INYOpools.com
I know dimensions of this o-ring, but is it round or square. The old one seems to be square.
This o-ring is round and not square. Over time the o-rings do tend to get mishappen so it is hard to compare the shape of the old to the new. If you have a Challenger pump then this is the correct replacement.