Pinball plastics take damage from the mounting nuts; they get scratched, and can deform.
This white nylon washer can be placed between a plastic and its post to protect the plastic printing and even out the clamping force. Use with a clear washer, or a second nylon washer, on top. A thin locknut may also be useful. Mosts post are #6 size, a few are #8.
Sold in a pack of 10.