I needed a small shelf for a small PC speaker sub. So why not make the brackets for the shelf since I already have a 3D-printer? So I did. They worked out nicely so here they are for all to print.

Measurements:
Top arm is 140mm (5.512in) long from wall to tip.
Bottom arm is 100mm (3.937in) long from shelf to tip.
Bracket is 10mm (0.393in) wide.

Screw holes are 3.5mm (0.138in) in diameter and the screw head counter sink holes are 7mm (0.275) in diameter. Im shure you have something laying around that will fit. There are access holes for a manual screw driver for the innermost corner screws. A hole big enough for the bit extender of a power drill to fit trough would mean a wider bracket. Tip: Use an awl (Or whatever thin pointy thing you have laying around, a large nail works to.) and a hammer on the wall beforehand to make the screws easier to screw in by hand. It will also keep you from moving the bracket out of place. Or just apply generous amounts of brute force.