Abstract: An improved ball and socket-type coupling adapted to provide a tamperproof coupling between a tow arm of a towed vehicle and a support member of a towing vehicle, the socket thereof having a dome shaped portion adapted to embrace the ball in a conventional manner, said ball being connected to said support member by a bolt means, said bolt means having an upper non-threaded shank, a lower non-threaded shank, an intermediate threaded portion, and a bolt head connected to said lower shank remote from said intermediate threaded portion, said upper shank defining a transverse aperture therethrough passing through the axis of rotation of said bolt, a nut means having threads corresponding with said intermediate threaded portion of said bolt adapted to mesh therewith so as to sandwich said support member between said bolt head and said nut means, said ball defining a partially hollow interior opening downwardly, said ball further defining a transverse aperture therethrough intersecting said hollow interior at a righ