I have a 4 inch metal junction box with a 3/4" mud ring attached and recessed into the drywall in my garage. I want to connect an air compressor to this junction box directly without using a plug. What do I need in order to close up the junction box and have a hole for a 3/4" flexible conduit to run to the compressor?
Is it as simple as buying a blank metal 2-gang cover plate and drilling a hole in it? Is there something off the shelf that's actually made for this?