Both 2/4's have a hole drilled all the way through. The 5/8 threaded rod is held against the 2/4 with a nut and large fender washer at each end. Very easy to adjust. Just turn one of the nuts. I used dental floss along the length of the main spar to check for level. The upper 2/4 has a small channel sawn across it for the rib rivets to fit into. Simple, works great.
