Our Nylon Shelf Pin and Shelf Hold Down set is used above an existing shelf. The loop shaped nylon hold down puts pressure on the upper side of the shelf to hold it in place. Shelves may be installed prior to the shipping of this item. The 2-piece set includes a P103 pin and a P113 hold down in a milky white color. The hold down is inserted over the shelf and compresses to lock the shelf in place. The shelf pin fits a 5mm diameter hole in 32mm system modules. The pin measures 5/16" long permitting insertion on both sides of a partition that is at least 5/8" thick.