Whoever owned my home before me put some nails in the mortar between what look like cinderblocks of some kind in my basement. Hence they're stuck pretty securely. I expect they could hold a lot of weight. (I haven't tested that theory.)
Nail heads are about a 1/4 inch (maybe slightly larger) in diameter. Several exist in various places on the basement wall. They stick out from the wall around 1/8 to 1/4 of an inch.
My cats (about average size for adult males; I think the largest might be 13 or 14 pounds) love to explore and to be up high, so I am trying to figure out how to create cat shelves (or a walkway or stairs or a climbing path or something) in the basement that will attach securely to those nail heads. These would stick out about 8 inches from the wall.
As I said, this is a cement/cinderblock wall, so screwing into studs is not going to happen here.
I have a bunch of scrap wood that I can use for this project, so what's the best way to attach anything to the walls here? Do metal brackets exist that I can screw onto the back of the wood in order to use the nail heads to support floating shelves? Should I get a specific router bit and cut appropriate slot-holes in the pieces of wood? Do I need to buy regular metal shelving brackets and a masonry drill bit and masonry screws in order to secure conventional metal shelf brackets to the wall?