This International Standard specifies rules for the identification of valve ports, subplates, control devices and solenoids for use in hydraulic fluid power systems. It applies in particular to valves which will be developed in future with two and three ports, where today's practise of marking valve ports is different. Table 1 therefore does not refer to components which are standardized in ISO 5781, ISO 6263 and ISO 6264. Identification rules as specified in this International Standard apply to those ports which provide the connection between two valves or between a valve and a pipe. The rules are consequently valid for the valves themselves when mounted in-line, and for the sub-plates on which the valves are mounted when such a type of mounting is used.