Proprietary two-piece string retainer (with 2 screws) for use on all Overhead travel bass guitars for both wood or carbon fiber. POM Material, two-piece. *This is an upgraded design with increased thickness and strength to replace thinner string retainers used on earlier models. This is suitable as a retainer replacement for OB660, OB660M, OB660F, OB660FM, OB660R2, OB660P1, OB660G1.