The Genuine BMW A/C Line O-Ring - 64539284850 is a small, circular rubber ring specifically designed for use in BMW air conditioning systems. It is used to create a tight seal between the A/C lines and other components, preventing refrigerant from leaking out and ensuring efficient operation of the A/C system. This O-ring is an authentic BMW part, made from high-quality materials and designed to fit perfectly in the designated space. It is an essential component for maintaining the proper functioning of your BMW's A/C system and should be replaced if damaged or worn out.