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