This is a universal ball and socket system I designed to mount small speakers, but I imagine there could be lots of uses. The center link is a 1/4" X bolt, length to suit.
- Update: Per Cyclone's suggestion below, I added a double socket piece to make an "elbow". I mocked up what could be a helping-hand device. Thanks Cyclone!
The cap and ball should be flipped over to print (threads up on the cap, hex up on the ball). I used 3 shells for strength. You need to work the threads on and off a few times to get them working freely. Be careful, as you can scrape your knuckles on the sharp edges turning the nut on and off!