Sorry, didn't mean to be gruff,
But I saw Clem take his rifle to the shop one time, and darned if him an Bubba didn't get a 1/4 x 28 nipple to thread in there, Clem said it tightened up real good too.
Clem's had a glass eye now for just under a year, he say's once the socket get's use too the prosthesis they can go back and match the size an color better.
He gave up Muzzle loaders.