holes while the rivet is red hot; consequently, the holes are drilled or punched 1/16 inch larger in diameter than the nominal diameter of the cold rivet.

Rivets are manufactured with one whole head already fixed. The rivet shank is cylindrical and the second head is formed by driving it with a pneumatic hammer. The rivet set, which is inserted in the end of the hammer, has a cavity of the proper shape to form the head of the rivet. Most Structural rivets are two full heads (fig. 1-53). Manufactured heads of rivets may also be obtained in countersunk shape to fit into holes countersunk in the material to be connected. When a driven countersunk head is to be formed, the rivet is driven with a flat-ended rivet set to fill the countersunk cavity in the material.