The abutment structure consists of a first element pivoted to one of the opposing sides of the seaming board and an opposing second element pivoted to the other of {HEAD ~ the opposing sides} of {TAIL ~ the seaming board} 
The abutment structure consists of a first element pivoted to one of the opposing sides of the seaming board and an opposing second element pivoted to the other of { HEAD ~ the opposing sides } of { TAIL ~ the seaming board }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL