The hole and rebate is made with a special hole cutter that matches the plugs. There’s a smidge of a gap around the perimeter of the plug... but even linoleum would cover and not show through.
It’s for a loft conversion
I need to get pipes under the floor before walls are built.
It will have to be push fit
I can then make a hole and reach in to connect the rad pipes
You can put the plug back into the hole but of course firstly you need something in place to support it from underneath. Pass a short bar of wood through the hole and screw it on straddled across the hole from underneath so that the bottom of the plug has something to attach to. I usually just glue the plug onto the bar but not onto the surrounding boarding. Therefore you can always unscrew the bar with plug attached in case you need to access the hole again in the future.