BS 4320 is a British Standard that provides guidelines for the dimensions and materials of sealing rings for hydraulic and pneumatic systems. This standard covers various types of sealing rings, including O-rings, quad rings, and back-up rings, and specifies their dimensions, tolerances, and material requirements. By adhering to the specifications outlined in BS 4320, manufacturers can ensure that sealing rings meet the necessary quality and performance standards for use in hydraulic and pneumatic applications. The standardization of sealing ring dimensions and materials helps to promote compatibility and interchangeability across different systems, ultimately contributing to the efficiency and reliability of hydraulic and pneumatic equipment.