A rivet before being driven is a simple cylinder finished at one end with a head. Various forms of heads are shown in Fig. 121. The point of a rivet is formed when it is driven, while the rivet is hot. Various forms of points are shown in the sketch. A tap rivet is not really a rivet, but a form of screw. After being tightly screwed in place and secured, the square projecting portion shown in the sketch is cut off leaving a flat or flush head. Tap rivets are used for connecting thin to relatively thick parts.