Ball mount (shown with Vise Clamp posted by cgongora69) http://www.thingiverse.com/thing:186545
Provides a stable base for a variety of vises or clamps could be used to mount a small camera also.

Made in 3 pieces to avoid need for supports and make assembly easier
Recommended material: ABS.
Set raft and supports off for all pieces.
Set infill for base and vice mount to 30%
Set infill for Ball Clamp to 60%
Print all 3 parts.
Drill and tap for 6-32 screws in the bottom of the vice or clamp you wish to mount. Bolt pattern is 10mm X 30mm on center.
Attach the "vice mount to your vice with 6-32 screws
The ball on the base may require a bit of light sanding, but keep it light or the clamp may not hold well.
Snap the Ball Clamp onto the ball on the base. (a few drops of Isopropyl alcohol will make it slip on readily)
Install a washer on a 6-32 X 1.25" screw and insert into the ball clamp. Install a washer and wing nut, level the top of the ball clamp and tighten to lock in place
Glue the vice mount assembly to the top middle of the ball clamp allow to dry for at least an hour.
. Mount can be screwed to a small board or work bench or glue a sheet of rubber gasket material to bottom for non-slip desk top use.