{HEAD ~ An actuator knob} is manually accessible to {TAIL ~ the user} and may be fixed axially to the outer housing 
{ HEAD ~ An actuator knob } is manually accessible to { TAIL ~ the user } and may be fixed axially to the outer housing
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH