Abstract: A portable coupler which can detachably fit into opposing corner fittings of adjacent freight containers for joining the containers into an integral unit is disclosed. The coupler includes a unitary tension spindle member shaped at each end to fit into and latch onto a standard container corner fitting. In use, one end of the spindle is fitted into an end opening of the corner fitting of a first container and the spindle is then moved longitudinally to engage and hook into the opening of an opposed end corner fitting of an adjacent container. A pair of bearing rings are fitted about the spindle, each formed with a bearing face to bear against the external face of an opposed container corner fitting. Both bearing rings are engaged to a common outer collar ring that may be manually rotated to separate the bearing rings and simultaneously provide a compression force between the corner fittings of the joined containers and a tension force in the spindle member hooked into both containers.