This is a 2" hole and aluminum cover at the bottom and top of my mast. It's purpose is to allow access to cables and connectors without dropping the mast. Holes were made with a 2" hole saw. The wall thickness of the mast measures 0.165".
Because the holes aren't located somewhere in the middle of the length of the mast, they don't weaken the mast to bending forces.
Cover plates are 1/16" aluminum with four SS screws. Screw holes in the mast are tapped with 10-23 threads.