The Sonex Upper Cowl is believed to be the single most difficult part to fit - and most importantly install. Per the drawings, the cowl is intended to fit under the windshield skirt, and then held in place by fasteners from the top. I decided to fabricate a "shelf" for the upper cowl to rest on during installation. I want the top of the cowl to align with the top of the windshield skirt - so, I needed a spacer the same thickness as the cowl. My cowl measures between .100" and .120" - so, a .125" aluminum strap is almost perfect.