This 3d print will fit a 4mm ring normally found at hobby lobby. We used the 100mm ring and
cut out a section until it would not vise on to our head. Then using a hot glue gun we are able to secure the ring from falling forward or backwards. some reaming is done to ensure there is a tight fit... I use a drill bit and just turned it by hand until i was able to have a snug fit with the
3d printed part and the cut section of the ring.