This is a heavy duty rivet, tubular or hollow – either name fits.  Steel with zinc plating.  Head is 7/16″ in diameter and the slight dome is raised 1/16″.
Shank or tube length is 5/16″, outside diameter of tube is 1/4″, inside diameter is 3/16″.
RVT-106  50 Pack for $6.00, USA shipping included.