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