17-0003 Adapter
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.
0491387 170003 Adapter MW
NOTE:
(Adapter) For screw-on radiator caps (standard thread)/Series: E28, E30, E31, E32 engine: all, except M51 Free only for motorcycle!!! [Discontinued]
Courtesy of BMW OF NORTH AMERICA, INC.