This kit includes one upper aluminum disc and the new reversible 1/4'' 3/8'' bolt. It is a convenient solution to upgrade to the latest version of aluminum discs and bolts. All aluminum discs include the Safe Lock material that reduces vibrations and improves the locking grip between head and disc. Furthermore the disc, together with the new bolts, allow a faster and more secure operation. It can be locked in position without the need of additional tools and the special shape of the bolts prevent it from accidentally falling into the columns.