HO Athearn F unit Connection Kit (black). For Athearn Blue Box locomotives. Comes with #6100 close coupling draft gear boxes and diaphragms for the rear of two A Units or one B unit. Close the gap with our innovative injection molded operating diaphragms. This easy to assemble kit turns a diesel lashup into convincing scale power units. Diaphragms stay connected in turn radii over 24 inches and have no minimum radius for smooth operation.