This is the seal that goes around the bottom of D and S series couplers. It creates the seal between Sankey couplers and the D and S series keg collars. If this seal is dry and cracked or has gouges it may not make a good seal.
Don’t hesitate to contact us if you have any questions about this or any other part we carry. We want to help you get your order right the first time and to keep your project underway.