Adjustable z-limit for Rigidbot with Peter Stoneham linear bearing holders

This mounts on top of Peter Stoneham's linear bearing mount on a Rigidbot. An M3 socket head cap screw threads through the part to make contact with the z limit switch allowing for easy micro-adjustment of the z limit. This was inspired by Pureluck's design ( http:www.thingiverse.com/thing:781168 ) for the original Rigidbot plastic linear bearing mount, but redesigned from scratch to fit Peter's stainless mount.
The mounting holes are slightly oversize for the 3 mm mounting bolts. The intent is to use washers under the nut or bolt head and compress the part to the frame. The adjustment bolt should thread nicely. Put a pair of nuts locked together on the end of that bolt to make clean contact with the limit switch.