[rotorwrench]

Willkie button plugs are available for different size holes. They are used in the aviation industry to cover unused switch & circuit breaker panel holes and in areas where an access button is needed through sheet metal for inspection or adjustments. I think Aircraft Spruce & Specialty has them. They have bendable fingers around the inside edges to hold them in place and can be sealed with RTV. THe original design is metal but some are now being made from plastic.