These are brass-plated steel hollow post rivets, meant to be set with a splash anvil or a tool like the RS-0302 tool we sell on our Tools page.
Head diameter is 5/16″, tube length is 3/8″, tube diameter is 1/8″.
If you follow the Rivet Rule of Thumb these are best used for joining together 1/4″ of material or less.
RVT-129  Bag of 100 for $8.00, USA shipping included