This RibMount™ System XL Tall mounting base is custom made specifically for buildings with metal rib siding (AG-Panel), perfect for mounting exterior wall lights with an elongated backplate. The RibMount™ System XL Tall mounting base allows the exterior light 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" Wide x 1.5" Thick (Variety of lengths available) with 1" center hole. IMPORTANT: Select routed offset distance from center in dropdown menu ("X" dimension in drawing) and overall length dimension ("L" dimension in drawing). All electrical components should be installed by a qualified professional.