I use Barracuda's formula but I add another step. I beleive medium fuel line is 3/32 OD. So I drill a 3/32 hole in the cowl where the screws go through. Then I slice off a piece of fuel tubing just long enough to protrude from both sides of the cowl. These should press fit into the holes with a little protruding from both sides. When you run your screw into the nyrod, the tubing will expand on both sides of the cowl and become just a bit larger than the original 3/32. You now have an isolation mount with no metal touching the cowl. You don't tighten the screws really tight, just tight enough to expand the fuel line.