This is the original rear upper shock mount and bearing for 1999-2003 E39 525i/528i/540i Touring (wagon) models. It's the upper mount that locates the rear shock to the chassis of the car. BMW calls it a Guide Support. It includes a bearing that should be replaced if it shows signs of wear when replacing the E39 Touring rear shocks.
This is an OEM Guide Support manufactured by an original supplier to BMW for many shock and strut mounts (usually Continental Rein, Lemforder, or Corteco brands). As the OEM it meets all of BMW's original design, fitment, and performance requirements and is TUV approved. OEM parts are the best alternative to more expensive Original BMW parts because they are virtually identical without the inflated price tag. This part has a two year warranty.
BMW Fitments:
5 Series
E39 (97-03) > 525i
E39 (97-03) > 528i 97-98
E39 (97-03) > 528i 99-00
E39 (97-03) > 540i