This product is a plastic end cap for our 1" Wide Aluminum Extrusion with Square Translucent Diffuser to give your extrusion a clean and finished look. This end cap snaps perfectly in to place when the extrusion cover is 0.78" - 0.98" longer than the extrusion (see photo for reference >>). This product is sold individually, extrusions sold separately. With proper extrusion sealing techniques and use of outdoor cover this cap can be exposed to outdoor elements.