Yes, this item is paintable.
The hole pattern is both 3" and 4". The cover it's self is 5" around.
Not sure. I would expect a seal ring would be required.
These knockouts are for boxes that are smaller than the pre-drilled holes. You need to drill them out and drill the outside for a counter flush screw configuration. Then you install the plugs over the original holes.
On Jan 23, 2019 they provided this answer to another question. "This cover has two sets of holes on it. One set is 3.5 in. apart and the other is 2.75 in. apart. So depending on how your are set up, this may work." I hate to assume but that's what I'm going to do and say that this is probably correct and the 3.75" was a typo.
This cover has two sets of holes on it. One set is 3.5 in. apart and the other is 2.75 in. apart. So depending on how your are set up, this may work.
This item takes the standard screw at the top and bottom of a standard round cover plate. I am not sure of actual size.
Thank you for your question. Unfortunately, we do not make this item as a 3" diameter piece.