I just used the allen pack I had with me to tighten it the first time. When I got home I tightened it with a bigger allen wrench. It kept loosening on me when I was riding, and like previously mentioned, it eventually wallowed out the splines, hence replacing the whole assembly. This last time it happened, (Tuesday) I left it as it was and took it straight to the shop (actually my wife dropped it off so I didn't get a chance to talk to them). I'm going by there today to hear their diagnosis.