The dolly assembly is used to unwind the wound strip of material from {HEAD ~ the roll} and position it on the roof to facilitate its seam welding to {TAIL ~ an adjacent strip} of material 
The dolly assembly is used to unwind the wound strip of material from { HEAD ~ the roll } and position it on the roof to facilitate its seam welding to { TAIL ~ an adjacent strip } of material
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH