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