allen head screw on the Hayes MX rotor body is to lock the inboard pad adjuster, i.e. the larger 5mm bolt on the back of the rotor. You loosen the small screw, adjust the inboard pad with a 5mm allen wrench then tighten the small screw down to lock it in place. Don't forget to loosen the small screw before adjusting the inboard pad or you'll ruin it. And don't forget to tighten it back up when your finished or the inboard pad will back out after a ride or two.
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