Dear Dr. Hussain Hady,

I agree with what has already been said by Dr. François Blateyron .

I suggest to you, however, to take a look at the following notes / paper:

-Surface Finish Charts: Some values of surface finish By LJ STAR

Available at: https://www.ljstar.com/resources/surface-finish-charts/

-Complete Guide to Surface Finish Symbols, Charts, RA, RZ, Measurements, and Callouts by CNC Cookbook

Available at: http://www.cnccookbook.com.s3-website-us-east-1.amazonaws.com/Calculators/SurfaceFinishChartMeasureSymbols.html

-Scratching of Materials and Applications

Pradeep L. Menezes, ... Satish V. Kailas, in Tribology and Interface Engineering Series, 2006

Available, as a third paper (with an interesting table) at: https://www.sciencedirect.com/topics/engineering/surface-roughness-value

Good luck and my best regards, Pierluigi Traverso

Dear Hussain Hady

120 and 320 grit are equivalent to 133.4 and 53.4 micron respectively.

Micron = 11615 (Grit) -0.933

Best regards

Read this book Measuring roughness of surfaces in mechanics

Dear Mohammed Hussein j. H. Al'Atia where does the equation come from? Do you have any references?

Thank you,

Ilaria