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