1
Marshall Bulle: Trailer hitch ring lock. April 3, 1984: US04440005 (29 worldwide citation)

Two generally flat, circular plates, one having an attached threaded male cylindrical shaped extension and the other an attached mating threaded female cylindrical shaped extension are threaded together through the ring of a trailer hitch tongue until the plates are in contact with the ring and held ...


2
Marshall Bulle, Dale A Johnson: Trailer hitch lock. Donald A Jacobson, September 29, 1981: US04291557 (25 worldwide citation)

An anti-theft device secured by sliding the device over a ball-connector type trailer hitch which automatically engages the hitch by means of a spring loaded bolt, to obstruct access by the ball and prevent unauthorized use of the trailer. The device is removed by retracting the bolt using only a co ...