The steel shaft has a steel cylinder next to a thin rotating brass drum. A friction band goes around the drum and a planetary gear train links it to a steel disc. A brass end piece fits over the shaft and has an internal gear. The end piece comes off easily. This frontlash unit on the Bush differential analyzer compensated for the backlash in a given drive between the output shaft of the unit and input shaft of an adjacent unit.
A mark on the disc and end piece reads: 8.
Compare to 1983.3002.09, .10 and .11.