JOHNSON - Deadbolt Blockhead Trailer Coupler Lock For 2in and 2-5/16in Couplers. Strong. Tough. Simple. Hi-tech materials redefine the traditional lip engaging coupler lock. Extruded, tempered aluminum body provides superior strength to weight ratio, a distinctive look, and great value. Simple, rugged push-button lock mechanism. Fits flat lip style 2in and 2-5/16in couplers. Durable, exterior grade powder coat finish. Double-sided automotive style key makes for easy insertion and removal. Shuttered key opening prevents clogging and freezing. Uses standard DeadBolt key codes. Fits 2in and 2-5/16in lip-engaging, trigger style couplers. Fits BOTH flat lip style. Coupler should have flat around the bottom. Maximum lip width: 4-1/2in.