One more item that will make rib cutting fit exactly between the spars is to temporary assemble the spars with compression struts and there pads and then measure between spars to get rib measurement. My full size rib patterns have shrunk about an 1/8" lengthwise (print size or paper shrinkage) OK-- you know that the front spar's width on the rear side is 5-3/8" and the rib capstrip has an 1/8" deep grove for the rib--so the rib height at the rear of the front spar is 5-3/4". measure the same way for the rear. Hope this helps. "Steze" http://community.webtv.net/smlangford/StevesFlyBaby