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A countersunk rivet is a type of fastener that has a head even with or below the plane of the connected material. What makes a countersunk rivet different from a standard rivet is the head. In a normal rivet, the head creates a rounded bump on the surface of the material. A countersunk rivet’s head is pressed down into a cavity on the material, removing the bump. These rivets are typically used for aesthetic reasons or to reduce drag on the piece.
Rivets are a type of permanent fastener. They are pressed through two materials and into a solid plate or block. When they hit the block, the penetrating end deforms and spreads out. This creates a permanent hold since the head and the deformed tail of the rivet are both larger than the hole in the material. Once in place, the only way to remove the rivet is to cut it from the work piece.
There are a variety of different head styles common in rivets. The most common type is a round head. A round head rivet has a head shaped like half of a sphere. When these rivets are in place, the head is plainly visible on the surface of the object. The other common types of rivets, such as pan-heads or flat heads, also stick up past a connected object’s surface.
The head shape of a countersunk rivet makes the top of the rivet flush with the connected object’s surface. This requires a specially formed countersunk hole. Other rivets are different because as long as they are the correct size, they will go into any hole. A countersunk hole widens at the top to allow the head to move down further. It effectively lowers the connected surface down so the top of the rivet is flush with the material’s surface.
Both the countersunk rivet and hole have the same shape. This common shape allows the rivet to sit down in the hole but stay flush with the object. In nearly every case, the hole and rivet head are shaped like a funnel. The sloped edges hold the rivet better than straight edges and make it less likely that water or air will be trapped inside the connection.
Manufacturers use countersunk rivets to keep the surface of the connected object smooth. After placing the rivet in the surface, it is common to cover the surface over with a sealant or paint, completely hiding the rivet’s head. This makes the surface more aesthetically pleasing, since it can be totally smooth. In addition, it causes less drag than if air was needed to flow over a common rivet head, making these rivet coverings common in high-performance vehicles.