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Then I made the locking bar itself.  This fits into the two slots in the upper left longeron. Like a lot of the angle pieces that have legs over 1” long, the plans assume a smaller inside radius than the actual angle has.  In this case, the piece that will interfere with the radius cannot be trimmed down because it is a square tube and would no longer work. I made a slight modification to the dimensions of this piece to accommodate the real radius.