German Surface Finishes: Important Conversion Warning

Summary for german surface finishes Discussion

German surface finishes are discussed in terms of a possible 1-4 micrometer range, but the thread warns against assuming a direct conversion to U.S. roughness numbers like 32 or 63. David Meade asked how German drawing callouts translate, and Bill Boatright suggested the 1-4 values may be micrometers, noting that 1 microinch equals 0.0254 micrometer and that 1-4 µm converts to about 39.37-157.48 µin. However, Ted Mooney cautioned that it is too risky to guess, because the notation might refer to Rz, Rms, or something else entirely, even if the numeric range matches a microinch conversion. The practical takeaway is that the drawing’s finish symbol or specification must be identified before making a conversion.