There is a quicker and easier way to connect two aluminium extrusions. Simply thread the hole in the "end" of one extrusion. Then drill a hole in line with the threaded hole in the other extrusion. Put a round headed socket bolt in the threaded hole and let the head of the bolt ride in the T track of the other extrusion. With an allen wrench through the hole, tighten the bolt. The connection is very hard and just as good as any other connector. And much less costly. Watch it being done: kzread.info/dash/bejne/n4aKsZSmqcyqlsY.html