a first portion configured to engage with {HEAD ~ the inner cam surface} of {TAIL ~ the actuator knob} 
a first portion configured to engage with { HEAD ~ the inner cam surface } of { TAIL ~ the actuator knob }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL