Series 1, (Traveler) three piece ground level kit includes the 3 components required to fix the disc directly onto the tripod upper casting: the machined aluminum Safe Lock upper disc, new reversible 1/4'' - 3/8'' bolt and new retractable hook assembly. For series 2 and 3 the aluminum disc is the new Power Disc, that features an additional locking screw to securely lock the head on to the disc. The kit is a convenient way to update previous Gitzo tripods to the Ground Level Set feature. Important note: this kit can properly work with the specific intended series only. They are available for Series 0,1, 2, 3, Series 1 Traveler and Series 2 Leveling tripods only.