I needed to mount a small solar panel for a backyard fountain. The ball portion attaches to a 1.5" x 1.5" post with screws, then the cup snaps onto the ball and holds a protrusion on the panel. The lock screws down to hold the cup in place.
You can edit the boxes that attach to the post and solar panel for other uses in Tinkercad. Thanks Joshfitz for the swivel link!
Sprayed first with Rust-Oleum Painter's Touch 2X (White) as a primer, then with a textured stone spray paint.