{HEAD ~ two diametrically opposite sections} on said sleeve, each of said sections having recess means on said inside surface opening toward said axis for receiving one of the transmitter and the receiver and to permit radiation to pass through {TAIL ~ the body} between the receiver or transmitter; and 
{ HEAD ~ two diametrically opposite sections } on said sleeve , each of said sections having recess means on said inside surface opening toward said axis for receiving one of the transmitter and the receiver and to permit radiation to pass through { TAIL ~ the body } between the receiver or transmitter ; and
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH