ONE standard aluminum rivet. The industry standard for kayak assembly. All aluminum, corrosion resistant, strong enough for most, if not all, applications. Most often used to install strap eyes on deck. You need a hand riveter to install these, if you don't have this tool, or don't plan to get one, these are not for you. Use this link for dims: Specs For Rivet.
Inside view of finished rivet:
Related Article: Basics of Strap Eyes, Rivets and Well Nuts.