取消并替换第一版（1980年）。给出了适用于管道系统部件的DN（公称尺寸）的定义，如使用DN命名系统的标准所规定。提供首选DN值的列表。

Cancels and replaces the first edition (1980). Gives the definition of DN (nominal size) when applied to components of a pipework system, as specified in those standards which use the DN designation system. Gives a list of preferred DN values.