M4-thread Bed Mount for D-Bot Printer

This is a re-implementation of the bed supports for the D-bot printer, beefed up slightly and modified to use an M4 bolt and nut instead of M3, as the stock springs weren't giving the support I expected with a heavy 300x300 aluminum bed (5+lbs with the silicone heat pad and associated hardware).

Note: the bolt spacing is 1mm farther from the aluminum rail than the stock (6mm vs 5mm) because of the larger space needed by the M4 nut, so these aren't an exact drop-in replacement... you'll need to slightly adjust the arms of the bed for the alternate spacing.