34-3000 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.
0492471 343000 Holding sleeve MW
NOTE:
(Assembly sleeve) For inserting the piston with sleeve into the tandem brake master cylinder, dual circuit braking system [Discontinued]
Courtesy of BMW OF NORTH AMERICA, INC.