When I installed mine, I just eye-balled em and double checked to make sure both rails were the same and eye-balled em again and checked em again...Did that about seven times..Than stood there with drill in hand for about three hours and FINALLY drilled some holes....I did a lot of checking and fretting for nothing..They went on real easy. Any variance in the way they sit is removed when you tighten the bolts down. The fiberglass lids will adjust. Make sure you have rubber washers under the rack legs....I've had them on my tourer going on four years and have not had any problems...

Dave R