whereby, a transmitter and a receiver received in {HEAD ~ said recess means} can be pressed against diametrically opposite surface areas of {TAIL ~ a body protruding part} 
whereby , a transmitter and a receiver received in { HEAD ~ said recess means } can be pressed against diametrically opposite surface areas of { TAIL ~ a body protruding part }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL