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