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