They screw into the hub, they only work in drop outs that are not closed off. They don't work in 12mm or 10mm that are threaded (the threads of the bolts are too big to fit through the holes). The bolts have to be screwed into the hub when the wheel goes on so the dropouts can't have an enclosed bottom - if that makes sense. I also have a 10mm though axle I could put in the rear hub.