I used 4-40 nylon bolts into corresponding blind nuts with lite plywood spacers. Washers should not be necessary for nylon bolts because they stretch. Used nylon bolts on the cowl and they worked loose from all the vibration. I then cut thin strips of glow fuel tubing and used them for washers on the cowl. Ten flights later and not one has worked loose.

Used Robart hinge points from the start. This is the only way to fly.