This is a genuine BMW expansion tank hose designed for use in the 525i, 530i, 545i, and 645Ci models. The part number is 17127519247. It is a high-quality replacement hose that is specifically designed for these BMW models and is made from durable materials to ensure long-lasting performance. This hose is an essential component of the vehicle's cooling system, responsible for carrying coolant from the expansion tank to the radiator. It is a direct fit for easy installation and is an authentic OEM part from BMW.