**Your trailing arm ball joint (PN 33306852895) is located in the upper part of the rear trailing arm, acts as an attachment point for the upper control arm on non M cars, on M cars this is also used for the lower portion of the trailing arm** This ball joint acts just like a bushing except it is significantly more durable. Standard control arm bushings use deflection to control suspension movements. This ball joint design pivots internally and does not twist or bind like a standard rubber bushing would. This makes it more durable and makes for a longer service life. On non M cars this ball joint is used in the upper section of the trailing arm only and acts as a mounting point for the upper wishbone. On M cars this bushing is also used in the lower portion as well and acts as a mounting point for the lower camber arm. This ball joint can be used on non M cars in the lower portion as well.