WARNING: This page is about a different car, the 2013 BMW 550i GT, 2012 BMW 550i GT, 2011 BMW 550i GT, and 2010 BMW 550i GT. However, it is still accessible from the selected car via links, so may be relevant.
0492472 343050 Holding sleeve MW
NOTE:
(Assembly sleeve) With 22 mm diameter to insert the piston with sleeve into the brake master cylinder [Discontinued]