RigidBot Z endstop level adjuster

Z-Level adjuster for the original RigidBot 3D printer. This allows you to fine-tune the Z-level using an M6 bolt by hand. Adapted for use in combination with Peter Stonehams [stainless linear bearing mounts](http://rigidtalk.com/wiki/index.php?title=Linear_Bearing_Mount) and fastened with M4 hex socket bolts with the plastic gantry holders as seen in photos. It is possible that it would work with the original plastic bearing mounts, but I have not tried (please let me know if you do).

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