This is a heavy duty rivet, semi-tubular.  Steel with nickel plating which has aged to a nice, dull silver color.
Head is 3/8″ in diameter and the slight dome is raised 1/16″.  Shank or tube length is 5/16″,
outside diameter of tube is 1/8″ at the bottom, has a shoulder at the top end of the shank, inside diameter is 3/32″.
RVT-128  50 Pack for $8.00, USA shipping included.