Theft-prevention device for tractor-drawn trailers

Claim 1

For a tractor-trailer combination wherein the trailer has a downwardly extending pin on the bottom, the pin being adapted to fit an engaging plate on the tractor, a theft-prevention device comprising: a cover for said pin to prevent the tractor plate from engaging the pin, said cover having an interior cavity for receiving the pin, an opening through the cover to said cavity, said opening having an outer small-diameter portion and an inner large-diameter portion with an inwardly facing shoulder between said portions, a slot extending into the cover transverse to said opening and through the large-diameter portion of said opening, an insert member in said slot and of a shape corresponding generally to the slot, said insert member having a threaded hole therethrough in alignment with said opening, and a studbolt disposed entirely within the large-diameter portion of said opening and said cavity of said cover and threaded only into the hole in the insert member, said opening being unthreaded, the bolt being rotatable for advancement into the cavity so that the inner end of the bolt may move into locking engagement with a trailer pin, the other end of the bolt having means exposed through the small-diameter portion of said opening for rotating the bolt, and a removable lock plug assembly positionable in the small-diameter portion of the opening for selectively closing said opening to prevent access to the means for rotating the studbolt, the lock plug assembly including a cam member rotatable by a key inserted into the plug assembly to a locking O-rings. behind said shoulder.