I was using JamKo76's Polymaker rings, but the nub/tab was always hard to push in, and the rings were a little too thick to roll smoothly in my AMS. So I trimmed 0.4mm from the base of the ring to make it fit better without affecting the part that clips onto the cardboard spool. I also changed the nub/tab a little, made it smaller (my Polymaker spool's hole measures 4.1mm, so I made the nub 3.8mm). 

PS: These rings work great for Duramic spools too!

Let me know how it works for you!

Printing instructions

Set infills all to concentric, and on the X1C, it's a sub 10 min print.