Marine Grade EPDM Rubber with Brass Threaded Insert Listed As: Thread Size x Overall Length (Grip Range) Commonly used in Automotive racking systems, Kayaks, Motorcycle Windscreens, Hardware in Utility Trucks, Compressors and Engines Creates a waterproof seal and minimizes vibration and shocks - Vibration isolation helps to prevent rattle and pull-out Rubber Well nuts are a common choice for waterproofing holes where an attachment is needed.