Historical
ISO 4397:1993
Fluid power systems and components - Connectors and associated components - Nominal outside diameters of tubes and nominal inside diameters of hoses
Specifies two series of diameters: a series of nominal outside diameters for rigid or semi-rigid tubes, irrespective of material composition, and a series of nominal inside diameters for hoses made of rubber or plastic.
International Organization for Standardization [iso]