This is a bracket I printed to make a shelf. It uses a french cleat system so there are no visible screws or hardware.
It is very sturdy as it holds a 14"x40" shelf with 3/4" hardwood. It is modeled to look like an old cast iron bracket.
The Bracket FC has coutersinks in it to show direction. It also has a small hole at the base. This hole is to lock the two pieces together once mounted. Use an M4 set screw through the L bracket into the Bracket FC to lock together.