these black alloy keymod or MLok picatinny 21mm wide flat base rails fit any keymod / M Lok platform or handguard quad with mounting screws so you can use bipod, light, laser, grip etc. Two length options; 1) 4 slot, 40mm long, 21mm wide, 9mm high or 2) 5 slot, 55mm long, 21mm wide, 9mm high