Firestone Ultra-Trim External Joint Clip Trim, These trims are often used to provide a clean and finished look in a middle join between two curb or gutter trims, as well as to ensure proper waterproofing and sealing. Firestone's external joint clip trim products are typically designed to work in conjunction with their EPDM roofing systems and other roofing materials. These trim pieces are often made from durable materials such as EPDM rubber or plastic, and they are engineered to withstand exposure to the elements and provide long-lasting performance.