I installed these tracks and cars on the cabin top for use with my 150% Genoa on a CDI furler. The tracks are thru bolted. I used acorn nuts on the inside of the cabin. They work okay, but they had to be installed inboard of the lifelines, which makes them less than ideal. But they do provide some versatility. I may still install tracks on the cockpit coamings, so I can get better sail shape.