My wife takes care of kids and she bought an Exer Saucer from someone cheap because they had misplaced one of the pieces that attached to it. She figured I could make her a replacement. So, I took out one of the other ones, went to TinkerCad, (thank you TinkerCad!), and designed a piece to fit into it. She wanted a ring on it so she could attach a set of toys to it for the babies to play with.

I printed it on a CTC Dual Bizer using M3D ABS-R. I printed without raft, but with supports. (Yes, that did make for a bit of cleanup, but it wasn't bad.). I also printed it at 90% infill, (I figured babies aren't too strong, but I wanted it to stand up to time and time again of pulling on it.)

You will have to shave off a bit of the corners on the two retaining pieces on the side that push in to insert, (I forgot to make them rounded), but that is not a problem either.

If anyone needs to replace one on their Exer Saucer, I hope this work for you. (You could possibly use it to make anything on the top by editing it in a CAD program.)