Spring and plunger from the DRITZ 1-1/4" cord stop (available in black, white, and translucent). Use pliers to squeeze​ the outer casing on the solid sides of the DRITZ stop while pulling the plunger, should come right out (don't lose the spring!). The fine detail on the cap model barely shows up on a 0.5mm nozzle printer, still, it gives you some clear delineations to paint. I haven't tried a resin print of it, I doubt it would be strong enough for real use. Maybe a 0.35mm printer will do better.