They come with a rubber shim to fit small diameter tube like rear racks are made from, and the clamp works just like a hose clamp -- just keep tightening the largest of the screw adjusters and it will keep getting smaller until it fits. If you need to, mount the clamp on the rear-most vertical support for the rack, and then adjust the angle of the part that the light clips on to (also separately adjustable) so that the face of the light is completely vertical. The part that the light clips on to can also be inverted if needed. Basically, this thing is capable of infinite adjustments to fit anything. I have bought two of these in the last 6 months (lost the first one, bought another) and they both came with the same clamp, so I'm assuming you got the same clamp too.[/QUOTE]

ginsoakedboy, thanks for the description, but do you have any pics?