The classifying openings permit {HEAD ~ material} which is already smaller than {TAIL ~ the size} of the openings to fall therethrough, thereby bypassing the comminution apparatus 
is smaller than
The classifying openings permit { HEAD ~ material } which is already smaller than { TAIL ~ the size } of the openings to fall therethrough , thereby bypassing the comminution apparatus
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH REL OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH