When the actuator is pushed down, {TAIL ~ the downward movement} is controlled by the interaction of {HEAD ~ the slots} with the guide rails 
When the actuator is pushed down , { TAIL ~ the downward movement } is controlled by the interaction of { HEAD ~ the slots } with the guide rails
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH