ˈrock-shaft
[rock v.1]
A shaft which merely rocks or oscillates about its axis in place of making complete revolutions; esp. one working the levers connected with certain valves in some forms of engines.
| 1875 Knight Dict. Mech. 1960/2. 1896 Cosmopolitan XX. 421/1 On the bottom of the vehicle, in front of the operator is a rock shaft, upon which the operator places his foot to manage the vehicle. |