This is a spacer for the Moonlite Focuser. I have a Skywatcher MN190 telescope and the spacer that came with the Moonlite focuser was 13mm thick, which was fine until I decided to add a filter wheel at which point I needed a few more mm of back focus so I removed the 13mm aluminium spacer for a 3D printed one of 3mm.

Critical focus on the MN190 is 0.08mm meaning that if you move from the focused position by more than 0.08mm your image will be out of focus, so any spacer between the focuser and the telescope needs to be perfectly parallel or focus one side of the detector might not be focus the other side of the detector, what we are looking for is a uniform distance across the spacer varying by less than 0.04mm, to acheive this I recommend that you print on a level bed and include a raft.

to see results this image https://flic.kr/p/24Jf5yV was taken with the spacer in place

Yes

doesn't matter

100%

Print with a raft to help ensure a uniform thickness