I purchased a large 15x15" piece of 1/4" (6 mm) tempered glass to use a print bed and needed a way to safely support and secure the bed on a moving gantry. The system also allows for 3 point leveling. This system includes a glass clip and a mounting base. The base is fixed in positon while the glass can be removed from the base without removing the clips. This allows for easy cleaning and parts removal without affecting the bed leveling.

This setup uses M5 hardware:
3- M5x8 Cap Screw
3 - M5 tee nuts
3 - M5x35 hex bolts
3 - M5 nuts - the narrow the better
3 - springs (1/2" x 7/8") in my case.

The knob used was the M5 nut loose from here: http://www.thingiverse.com/thing:641854

My printer has 20x20 OpenBuild V-slot rails for the gantry. The base is secured to the rails using a M5x8 cap screw and tee nut. The hole diameter in the base and the loose fitting nut in the knob provide some degree of freedom for adjusting the bed. The degreee of freedom works well on a large bed like this, but probably not as well on smaller beds. I haven't tested this but

Basic directions:
Print the parts
Mount the bases
Assemble and install the glass clips
Mount the glass

The base locations will need to be adjusted based on gantry layout, glass size, etc. I recommend keeping the bases a bit loose in the rail until you set the glass and then lock them down. Keep the bases near the edge of the glass so you can get a allen wrench under the glass to tighten them down.

Note: The base shown above was an earlier version and not the final version. The hole is big enough for the M5 hex bolt but doesn't provide for bed angle adjustment.