I am trying to construct different forms of space frames both movable and stationary. One of the items I have found I need is a ball and socket joint. This thing provides the socket, and places them around the perimeter of a disc.

It's parametric, in that you can construct a new disc joint, with any number of sockets, with any radius on the socket. The thickness of the disk will automatically adjust based on the radius of the socket. You will need to manually adjust the radius of the disc though.

In the pictures here, I've used the socket joint to construct my favorite tetrahedron. You could create any space frame structure using this discjoint, with different numbers of sockets based on the needs of the structure.

Also included here is the ball cap that fits on the end of a 5/16" (8mm) rod.

The socket fit is very snug, and as you put all the balls in their sockets, the whole joint becomes more firm. This is a good general construction piece, and the ball/socket combination makes for a nice movable joint if your construction needs that.

UPDATE: 14 Dec 2010
Added discballjointslender - half the thickness, with an axle hole

Figure out how many sockets you want on a disk.
2) Print out disks that have the number of sockets you need
3) Shove ball caps on the end of your rods
4) Shove the rods into the sockets
5) Assemble your frame
6) Rejoice!

The default here is 5/16" diameter