指定安装伺服阀的表面尺寸，以确保互换性。主要适用于电液流量控制伺服阀。此外，还可用于压力控制伺服阀。如果阀门用于三端口应用，则可省略任一维修端口（a和B）。

Specifies the dimensions of surfaces on which servovalves are mounted in order to ensure interchangeability. Applies primarily to electrohydraulic flow-control servovalves. In addition, may be used for pressure-control servovalves. If the valve is used in a three-port application, either service port (A and B) may be omitted.