Loosely assemble the two sides of the boom with the copper spacers. Two people are recommended for this step as the boom can tip over easily without the circular base attached.
Glue the three "L" pieces and place it between both boom pieces as shown in the picture below. Mark the two holes in piece "L" where the 1/4" carriage bolts will go through the piece from one side of the boom to the other. Drill the 1/4" diameter holes through "L".