This fits into a 1'' optic mount that is not rotary and holds a 1'' optic so that it can rotate (roll). It is a zero pitch screw and nut, printed around each other, with cylindrical tubes for the optics. Very handy for polarizers, waveplates, etc. Print this small cylinder down.
NOTE: Depending on your printer you may need to forcibly move the joint the first time after printing...'cracking' plastic support where the printing may have led to the bearing freezing. After that, your good to go!