a pair of {HEAD ~ shafts} provided at one end with the paired horizontal rollers and at {TAIL ~ the other end} with mutually engageable gear wheels, 
provided at
a pair of { HEAD ~ shafts } provided at one end with the paired horizontal rollers and at { TAIL ~ the other end } with mutually engageable gear wheels ,
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH