Pien

To secure a rivet into place by hammering . A mushroom of the rivet material is formed and the materials to be joined trapped in between the rivet head and the mushroom. A round face is used to make the shape, and sometimes if a soft material is to be secured to a hard one (such as a leather strap to a piece of armour) then a rough washer might be cut and placed under the mushroom side of the rivet.