Marine grade pop rivet. Comes with water sealant on the inside part of the rivet. Depending on your rivet gun, 1-3 squeezes will set the rivet properly. Once the rivet goes in, sand off the remainder if there is a sharp edge. Practice on some spare material is recommended before use. Sold individually.
Item Number: BHW-WSR
Works great for installing rod holders on places where you don't have back access. Make sure to break the rivet properly: https://www.youtube.com/watch?v=WPwNsQMnx88