This is just a rack to hold four R8-style tool holders such as ER collets, endmill holders and drill chucks. This rack is suitable for tools with a largest-diameter of 62mm (2.4in) to avoid interference. Racks can be screwed together using M4 screws to create a larger support structure. It is recommended that the rack be fastened to a work surface using a dot of super glue on each corner or a right angle bracket in the lower M4 hole. I did not add screw holes for holding the rack down as I wanted the model to be printable without supports.