I installed a new Raymarine i40 depth instrument where a large 1980's depth instrument had been, leaving a large hole. I started thinking of turning a bowl on the lathe to cover the new instrument from the inside. The i40 depth had a long threaded stud it uses to mount, anything that catches that stud will work if secured with a nut. I realized that wooden salad bowls were roughly the right shape so I went searching for bowls on Amazon. The dimensions for bowls are approximate because you are not supposed to care so it ended up a little small, instead of resting on the surrounding bulkhead it rests in the hole in the bulkhead. A good color match for about six dollars.
A second issue with this installation was that I decided to add some screws after the Starboard filler disk had already been fabricated and the instrument was already sealed to the disk. Hard to do without a center to work with. I made a paper ring and divided it by folding it while holding it up to a light. Sixteen good divisions later I was able to lay out my screen pattern. This is a surprisingly accurate method.