Tubular Rivets & Washers (8mm) 5/16" Goldstartool.com carries tubular rivets in (8mm)5/16" and in the following finishes: Silver, Bronze, Gold, and GunMetal. These are solid rivets that are used with leather, fabric, and other materials. The rivets are measured by the cap size. As a rule of thumb, you want roughly 2mm of the rivet post sticking through the material on the other side. We also sell the rivet setters and presses to help with installation. Cap Size (8mm) 5/16" x Tube Diameter (4MM) 5/32" X Length (10.5mm) 7/16" Available in Silver, Bronze, Gold, and GunMetal. Sold in pack of 100 & 1000.