The #6 cap just before it was dropped into place. The shining spots are clearance grooves that we ground a little deeper than they were when taken apart. There were already grooves here, but i do not think they are really "factory", but simply chewed into the caps by the ring gear teeth. The extra hole next to the middle bolt hole is for the insertion of the oil line to lube the lower, or axle sleeve mentioned above.

Photo by Bill Liebman