With a bunch of reloading stuff I picked up is a bushing that is in a Herter's box, Tried it in my RCBS A3 no luck. Got out the caliper and the thread pitch gauge and it shows a diameter close enough to be 1.25 OD, thread pitch, well lighted and under low magnification looks like 18. It's looks brand new, it's knurled, not a hex head like the RCBS bushing.
Any clues on what/who's magic reloading machine it goes on?
Standard die threads right in.