Each pair of bracing members defines {HEAD ~ a guide} for the displacement of the end supports of the support roller for {TAIL ~ the lower belt} 
for
Each pair of bracing members defines { HEAD ~ a guide } for the displacement of the end supports of the support roller for { TAIL ~ the lower belt }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL