Bulb-Tite rivets are designed for use in thing sheet metal or soft materials such as plastic or laminates. This rivet has a rubber sealing washer under the head and "bulbs" out when it is pulled creating a weather tight seal. These come in aluminum and offer superior shear and tensile strength. 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.