See Hobie Cat Catalog 2002 online http://www.hobiecat.com/cats/partset.html

From the price list, the rivet is 6-10 PN HD Monel. The backup washer is curved to fit the lip on the hull. As an alternative to Monel, use stainless steel. Make sure you have a heavy duty rivet gun, the large type with long handles. The rivets must be set correctly with a tight fit, so there is no slop between the track and the hull. Good luck. Caleb