Master Coupler Latch Lock - Trailer Locks 1471 This Master Lock protects and guards against tow-away theft. The lock works when the trailer is either connected to the tow vehicle or when the trailer is unattached. The lock prevents the coupler latch from moving, therefore preventing either the coupler to be removed from the ball, or not allowing a ball to be placed into the coupler. Fits UFP and surge brake couplers. Pin length or dimensional fit is 3-1/2" wide with a 9/32" diameter pin which is a standard size on virtually all couplers. Chrome plated for improved wear and corrosion resistance. It has a precision 4 pin tumbler mechanism that resists picking Weather Tough seal and water tight cap protects the lock from the elements