An activation button exposed through the top of {TAIL ~ the assembly} is depressed to actuate {HEAD ~ a switch assembly} which, in turn, actuates a drive mechanism 
An activation button exposed through the top of { TAIL ~ the assembly } is depressed to actuate { HEAD ~ a switch assembly } which , in turn , actuates a drive mechanism
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH