This is a modular mounting system for Milwaukee tools. I have provisions to mount each rack to the neighboring one using #10 hardware, and the racks can be mounted to either the underside of a shelf, or to rails with t-nuts on a 6 inch spacing (5/16 hardware). This model is for the whole line of MIlwaukee m18 batteries. I have tested this on everything from the cp3.0 to the hd12.0