McGard UHS security nut set (4 nuts + 1 key). To increase security, the UHS series nuts and bolt head are equipped with a rotating ring. which makes it extremely difficult to open them without a special key. The UHS series meets Thachams 4-level security category. Nut height 39 mm. Chuck diam 29 mm. Key size 21 mm. Do not use a compressed air wrench to tighten the security nuts! Each package comes with an ID number. You can order a spare chuck based on this code!