It's a metal cuff that tightens down with a flathead screwdriver (the kind you might use to attach a rubber hose to a faucet or pipe - hence the name). You can get one at your local hardware store for under a buck. You put on the wheel, close the QR hub so it's nice and tight and the lever is right next to one arm of your fork, then put the clamp around the fork and the lever and tighten it down, so that anyone wishing to steal your wheel will need a flathead screwdriver and a couple extra minutes.