My tool chest has center runners. Both the drawer sides and the chest sides are cabinet grade plywood. The grooves are in the drawers, and the runners are attached to the chest. In my case, I thought it was easier to mount runners to the case sides, and easier to build the grooves into the drawer sides, but either way works. Either of these construction techniques yields a more compact chest than if you attached kickers and runners to the case sides that wore against the tops and bottoms of the drawer sides, and that required drawer blades and some space between the drawers.