This Tool Holder is made with 3 boxes, two are glued in the third, the sizes are designed to fit them fine. For make them I use the openscad file "clone wars plate id" (user obijuan) adjusting some parameters.
You could use this three items alone or hold them to your prusa. To make that you must hold the RAMPS holder making two holes in the toolholder and using m3 screws and nuts.
With a prusa 2 must use the standard RAMPS holder, designed for m8 rodbar. The item is RAMPS-Holder (user michielh)
With a prusa 3 must use the scaled up RAMPS holder, the scale is 10% higher. This stl is included here. Is designed for M10 rod bar.
The pictures show you the final result. Enjoy!