What is meant by Rz 160 for raised face flange?

[Afifex]

Hello guys,
In the piping specifications for my company, there are three types of flanges:
1- Type C: Raised face Rz=160, machined,
2- Type D: Raised face Rz=40, machined,
3- Type E: Raised face Rz=16, machined

Could anyone explain what is meant by Rz for raised face flanges?

 

[rconner]

This is a specification for the required surface finish for the face of the flange. The R refers to roughness and the z for the e.g. statistical parameter of profile measurements used to assess same. You would find a lot more detail from many sources with a keyword search e.g. under "machine finish".