These bi-fold roller guides are constructed of steel, nylon and plastic components. They are commonly used with Kenna Frame bi-fold doors, but many other manufacturers also use this same size guide. These spring-loaded roller guides feature 7/8 in. outside diameter wheels that are 1//4 in. thick with a 3/8 in. outside diameter base. These guides mount on the top edges of bi-fold doors and require only a 3/8 in. Dia hole in which to insert. Use these top-mounted guides where rollers are missing, damaged or not working properly, to restore bi-fold doors to the ease of operation they were designed to have.