123 589 01 03 00 Box wrench bit - WS46.00-P-0015A
WARNING: This page is about a different car, the 2012 Mercedes-Benz C300, 2011 Mercedes-Benz C300, 2010 Mercedes-Benz C300, 2009 Mercedes-Benz C300, and 2008 Mercedes-Benz C300. However, it is still accessible from the selected car via links, so may be relevant.
FG 46/Set A
MODEL 107, 123, 124, 126, 170, 201, 202, 240
Use:
19 mm box wrench insert, 1/2" square for loosening and tightening the collar nut from underneath.