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