One of {TAIL ~ the drafting roll pairs} is a first drafting roll pair as viewed in {HEAD ~ the advancing direction} 
One of { TAIL ~ the drafting roll pairs } is a first drafting roll pair as viewed in { HEAD ~ the advancing direction }
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD