Yep, just the joint. I've got 2 sets of Sun Rhyno Lite rims, each of which has a visible joint just like that. They weren't very apparent at first, but as I put miles on the wheels they became noticeable. One wheelset has been retired to backup status, the other still being used on trails. With my 225 lb butt riding over rocks and roots, if it was a problem the rims would have come apart by now.