What indicates the size of a hose used in a hydraulic system?

The size of a hose used in a hydraulic system is indicated by the numerical designation on the outside of the hose. This designation typically includes measurements that correspond to the hose's diameter and pressure ratings, which are crucial for ensuring compatibility with the hydraulic system's specifications. These measurements enable operators and technicians to easily identify whether a particular hose is suitable for the pressures and flows required in the system.

The other options do not provide a reliable indication of hose size. The color of the hose may serve various purposes, such as identification or differentiation between types of fluids, but does not reveal any dimensional attributes. The manufacturer's label may include important information, such as material type and pressure ratings, but it is the numerical designation that directly assesses dimensions. Lastly, while the length of the hose is important for installation purposes, it does not indicate the size of the hose in terms of diameter or capacity, which is what the numerical designation specifically addresses.