I made it from 1/4" diameter steel rod. It’s just like the sling attachment you would find on a rifle stock, but it doesn’t swivel (no need to). The back end is threaded #10-24. The part is finished in Birchwood-Casey cold gun blue.
Make the post first and screw it on to the track, then mark the split ring hole location to get it orientated correctly.
My track is 1/4" thick Type 2 Gray PVC bonded to .080 thick 6061-T6 aluminum sheet stock. The thread goes all the way through and is flush to the back side when assembled. The track assembly is screwed into (6) threaded aluminum blocks attached to the inside of the gun box. I knew this would carry the whole weight of the gun, so I made all the load transfer points aluminum.
I WOULD NOT try this method with a cast resin track. I fear it would be far too brittle to carry the weight of the gun swinging at your hip.