There is now a version 2 of this that has a few useful modifications. https://www.thingiverse.com/thing:2843786

These parts can be used to make a Bath interferometer used to measure telescope mirrors. These parts were designed for a 15mm beam splitter, 7.6mm diameter lens, and 13.5 mm diameter laser pointer.

The parts were designed in Fusion360 and that model will be published. It has been parameterized to make lens and laser holders of different sizes.

You can also comment asking for another size and I can upload the .stl far a specific size.

These parts were printed in PLA.

The flat mirror can be glued with RTV silicone to the mirror socket. The cube is held by friction in the cube holder and is pressed into it to assemble it. It should only be pressed in by hand and finger pressure. It will be a firm fit. The screw for the socket is a 2-56 screw. All other screws and nut are meant to be 6-32.

There is a hole in the cube holder and base for a 8-32 screw to hold the cube holder to the base but that should not be needed.

a 6-32 screw not shown is used to attach the mirror ball to the base. A 6-32 washer is also a good idea between the head of the cap screw and ball base.