This is the V-Slot Spacer Block.  It was specially designed to be used in conjunction with the V-Slot Gantry Plate.  It allows you to raise the V-Slot Gantry Plate up away from the rail 12mm so that you can run transmission components such as a belt drive or threaded rod underneath the V-Slot Gantry Plate. 

• M5 tapped holes to allow mounting to the V-Slot Gantry Plate.  
• 3 holes that allow for mounting of full size OpenBuilds Wheels.

Download open source model

SolidWorks parts are here