

They would have the same coefficient of drag, correct, but the air resistance would end up having more effect on the lighter mass of the hollow sphere, so it would be slightly slower to fall.
Archimedes principle here is accounted for in the different weights. Everything that you can put on a scale is already being acted on by Archimedes principle in air.








Yeah, but unfortunately it has to protrude from the surface because the bit grabs the outside, which means you can also grab it with pliers. Not the best feature for a “security” fastener.