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