Nikon circular eyepiece insert

Threaded insert for nikon fm, fm2, fm2n, fm3a, fe, fe2 and probably others, eyepiece. I use this as a low profile screw to hold a small, cut to fit piece of acrylic from cheap eyeglasses from zenni to use as diopteric adjustment lenses for my cameras. much cheaper than buying first party pieces, and they sit so low profile they dont unscrew themselves over time. I added slots so u can put them in or remove them with a pair of spanners. I printed mine in petg. Might take a bit of finagling. Stole the threads from someone elses model for a similar use but I don't remember whose. credit to that guy.