The PH 18 consists of a cast aluminum plate with a formed protrusion on the back side designed to fit into the triangle created by the joining of the seat stay and the chain stay of the towing bicycle. The plate has a rubber backing to protect the bicycle frame. Four sets of polypropylene cord, springs and cord locks "tie" the hitch onto the bicycle frame when engaged with the cord stops on the cast plate. A PH12 rod end joint assembly is attached to the casting to provide the hitching point to the tongue clevis.
On earlier models, this hitch was sold with a ball and socket connection.
The casting is of 512 "tensalloy" aluminum.
This hitch does not work well with disc brakes. If one has a ball and socket type connection, It may be replaced with a clevis and pin. See: http://www.equinoxtrailers.com/store/item/241