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