I needed a thicker plate to mount a E3D V6 in place of the Hexagon hot end and this is it. The extra bosses with holes are to mount a part fan or other accessories.

I mount my part fan off of the left (square) one and have a support for the hot end wiring on the right-hand one. Holes fit a 3 mm bolt and designed without threads. Just cut threads when you screw in the bolt.

Update 5/3/16
I uploaded a couple pictures showing the use of the accessory bosses on top of the plate. The pictures show my new gantry design (not yet published) but the accessory bosses are the same.

Also uploaded the FreeCAD files so the boss hole size can be adjusted.