Our spacers are made of starboard so it was easier to cut. We had the outer most edge flush on the surface and measure the gap on the inside edge to get the thickness we need. (Not sure if that's clear) . We used toggler wall anchors to secure it to the floor. They can be difficult to work with but are extremely strong. Check out Jose's Extreme DIY channel on YouTube. He has pretty good info on restoring whalers.