The assembly consists of a black plastic platten on a steel shaft with a ratchet detent on one end. The square shaft at the other end is spring loaded. A separate metal collar fits over platten end with the square shaft. The ratchet detent is stamped with 54 which seems to be the number of teeth. No other markings found.
overall: 1 3/8 in x 20 1/2 in x 1 3/8 in; platten surface: 15 3/8 in