34-3050 Holding sleeve
WARNING: This page is about a different car, the 2011 BMW X6 and 2010 BMW X6. 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]
Courtesy of BMW OF NORTH AMERICA, INC.