Each of the pair of {TAIL ~ sensor block members} is provided with an inner surface having {HEAD ~ a vertically extending recess} 
Each of the pair of { TAIL ~ sensor block members } is provided with an inner surface having { HEAD ~ a vertically extending recess }
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD