 displacing adjustable pivot bars on two stationary ones of {HEAD ~ said frame engaging members} to apply {TAIL ~ pressure} to said frame members to ensure that the corners thereof are well connected and squared off; and 
displacing adjustable pivot bars on two stationary ones of { HEAD ~ said frame engaging members } to apply { TAIL ~ pressure } to said frame members to ensure that the corners thereof are well connected and squared off ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH