Coupler lock is best used for trailers; Works best with Straight Tongue Trailer Couplers Advance locking mechanism resists picking and prying Designed to resist rust and corrosion Fits most couplers 1-7/8 in. (48 mm), 2 in. (51 mm) and 2-5/16 in. (59 mm); Does not fit Gooseneck Trailer Couplers Includes one trailer coupler lock, two keys