Closed-end rivets or "sealing" rivets are used when a weather proof or leak proof seal is needed. This rivets unique design forms a seal when the rivet is crushed, allowing these rivets superior corrosion resistance. Countersunk closed-end rivets are made to go into a countersunk hole so that they will sit flush with the surface material. Grip range is the amount of material the rivet will be going through, not the actual length of the rivet, which will always be longer than the grip range.