One of the dust caps for my scope cracked and lost an ear.  This is a replacement for the exact size and shape of our model.  It is approx 40mm diameter and 28.5mm tall.

It's designed to accept the original clear plastic lens  (37mm x 1.5mm) printed into the part. The G-code has a pause built in at the place where the lens can be inserted and then the retaining ring is printed on top of it.

I also included a closed end version in case you don't have a clear plastic lens to include in the print.