Twice now it has just simply unscrewed itself and fell off on me as I was riding. Did I loose a lock nut or something? It doesn't look like the bolt comes out of the other side to attach any sort of nut or anything to. It seams that the bolt just works it way out. After the first time it happened I checked it every day before riding, so it doesn't take it long to come out, if it does. Can I just weld the **** thing together so it doesn't happen again?