It will be noted that {HEAD ~ the roller} 36 rolls along {TAIL ~ the side rail} 4 during the forward movement 
rolls along
It will be noted that { HEAD ~ the roller } 36 rolls along { TAIL ~ the side rail } 4 during the forward movement
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH