This RibMount™ System Large mounting base is custom made specifically for buildings with metal rib siding (AG-Panel) to assist with mounting exterior lights or other electrical junction boxes. The RibMount™ System Large mounting base allows the exterior light, or other electrical box, to be installed exactly where desired regardless of metal rib location. Material is PVC (paintable) and resists yellowing over time due to UV protection added. Actual dimensions are 7.25" x 7.25" x 1.5" with 1" center hole. IMPORTANT: Select routed offset distance from center in dropdown menu ("X" dimension in drawing). All electrical components should be installed by a qualified professional.