The hitch lock is coated with gold electrophoretic paint to prevent corrosion. Coupler Locking Hitch Pin's Application: Tow Trailer Boat RV Truck Car. Trailer Hitch Coupler Locking Pin Design: 1/4 Inch diameter tongue lock pin with effective length 3/4 Inch. Small size for easy carrying, you can keeping the coupler lock in your pocket or vehicle anywhere that is fine. Security Of Our Coupler Locking Pin: This trailer lock is made of high-strength steel to deter theft. How To Operate Our Trailer Tongue Coupler Lock: Spinning the flat key 5-7 times to open or close the hitch lock.