Phillips flat head machine screw for attaching bucket seat, seat back release catch on any 1968-70 Mercury Cougar or Ford Mustang including bench seat cars. Original screws are trilobed, meaning that they have triangle shaped threads instead of perfectly round. Helps with locking. We recommend using locktite or some other thread sealer when installing. Or at least check the torque after several weeks of use. 5/16-18 flat head machine screw, zinc plated.