The "Hook" attaches to the Flex Wheel or the White firm wheel for the MicroLux sander. The "Hook" allows the sand paper to be changed very quickly as the unit becomes a "Hook and Loop" system. The sandpaper is easily changed from one grit to another very quickly. The "hook" and sanding discs are actually cut larger than the blue flex wheel, by 1/2 inch to allow the sander to easily go around curved surfaces and up or down the neck of a curved gourd without cutting into the skin.