WARNING: This page is about a different car, the 2016 BMW Z4, 2015 BMW Z4, 2014 BMW Z4, 2013 BMW Z4, and 2012 BMW Z4. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
(Inner ring) discontinued, available as part of set of special tools only
Fig 1: Identifying Ring Minimum Set - Mechanical Tools AM (212182)