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