Advisor / ISO GPS reference / Rq
Surface texture parameter · ISO 21920-2
Rq (root mean square deviation)
Root mean square of the roughness profile height deviations.
In the shop
Rq usually reads somewhat higher than Ra on the same surface, so do not swap the two numbers on a drawing.
General shop guidance in our own words. The drawing and the standard it cites decide; verify on a sample part.
Typical finish by process and the turning feed and nose-radius formula: Surface finish guide.
Related surface roughness parameters
Ask about your drawing
Tell the advisor the feature, the tolerance on the drawing and the material. It answers with machining choices, brand-neutral.
Sources
Definition written in our own words and checked against engineersedge.com. Symbol and term names follow ISO 21920-2; we do not reproduce standard text. See the full index.