The Kegland Duotight 8mm (5/16") Female x Female One Way Check Valve is a high-quality push-in fitting known for its superior sealing capacity, attributed to its double O-ring sealing design. This feature ensures a tight seal, enhancing the reliability and efficiency of your gas systems by preventing backflow and protecting your equipment.  This is a one way check valve so be sure to check the arrow inidcator on the part during installation.