It can vary, Steve, that's probably why you haven't received a specific reply. If they are way, way aft, you'll end up in the vertical part of what is the backrest in the cockpit. Further forward it's at least three quarters to an inch thick. It seems that you're dealing with four screws, so I recommend buying an assortment and finding what works for you. As previously noted, the screws are in shear, so don't need to be too deep to hold the cleats.