[bojan]

This is central part, prism (or mirror) holder (the one I already had, made from PVC).
Prism is held in place by two nylon screws, and the diameter of the barrel is chosen to fit the prism which sits inside, precisely centered.
Collar diameter (to scope) was dimensioned to fit MTO-1000A, so I needed adapter ring to fit it to Celestron Visual adapter. If I needed to print this part, collar would include adapter.
Rotating part was printed as on image below.