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 conventional key. No tools or auxiliary parts are required to attach or remove this device.

This invention is designed to lock a trailer coupling, which includes a trailer hitch of the lever type and a ball-type connector. The coupling is locked by a locking-ball which is constructed by modifying a conventional ball to conceal the locking element, and how it provides the locking function. The locking-ball includes a substantially spherical ball in which a hardened steel bolt is threadedly disposed axially therewithin for vertical axial movement of the bolt through the upper surface of the locking-ball. The locking-ball is inserted in the socket of the trailer hitch, and the lever is closed in the "down" position so as to actuate a cam against a jaw, which jaw in cooperation with the socket, snugly holds the ball in position. The bolt is then advanced vertically by a key in mating relation with the lower end or head of the bolt, until the upper end of the bolt is forced against the inner surface of the socket, and the ball is forcibly biased within the socket against the jaw. When the ball is forcibly thus biased, it is held immovably in the socket, the lever cannot be raised, and the trailer hitch cannot be opened to permit the insertion of another ball.

A trailer locking device adapted to be fixedly inserted into the cup of a trailer hitch. The locking device, which can be in the shape of a ball, includes an outer shell made from a plurality of movable plates. Once inserted into the cup of a trailer hitch, a locking mechanism is used to separate or otherwise move the plates apart in order to expand the size of the outer shell. Once locked into position, the trailer locking device becomes lodged within the cup of the trailer hitch preventing a trailer in association with the trailer hitch from being stolen.

A trailer hitch lock for enclosing a trailer hitch to secure the trailer against theft. The trailer hitch lock includes a base plate, a set of locking plates pivotably mounted to opposing sides of the base plate and a locking mechanism for securing the locking plates together. A mounting ball is mounted on the base plate and is configured to engage the trailer hitch ball socket. The first ends of the locking plates are hingeably connected to the opposing sides of the base plate. The second ends of the locking plates and the locking mechanism cooperate to secure the locking plates together.

A security device for a trailer hitch or similar article which engages with an outwardly extending peripheral flange around the trailer hitch or similar article, and which includes an element which extends into a coupling opening in the trailer hitch or similar article, thus precluding removal of the security device from the trailer hitch or similar article. A padlock is utilized to deter unauthorized removal of the security device from the trailer hitch or similar article, and the security device includes means to protect the shackle of the padlock from unauthorized removal.