MASTER LOCK KING PIN LOCK FOR SEMI-TRAILERS, RV AND FIFTH WHEEL TRAILER – 387 THE MASTER LOCK NO. 387 HIGH SECURITY KING PIN LOCK SECURES THE KING PIN OF SEMI-TRAILERS, RVS AND OTHER FIFTH WHEEL TRAILERS TO PREVENT THEFT AND DETER BREAK-IN’S. INCLUDING AN INTEGRATED PADLOCK (NO. 5), THIS LOCKING DEVICE RENDERS BOLT CUTTERS USELESS AND THE HIGH-GRADE ALUMINUM IS LIGHTWEIGHT WHILE PROVIDING HIGH SECURITY.