What Do Multiple Triangle Symbols in Surface texture notes mean?

A. Sheldon:

What you are describing is a common but obsolete way to express a grade of machining finish. The idea was to represent rough or first machining operation by one triangle (triangle symbolizes the turning cutting tool). Two triangles meaning two passes of the tool and hence finer finish. Normally four triangles require a grinding operation and a roughness of between 32-16 microinches RMS. But this has to be agreed upon with designer and manufacturer.

P.S. Have you looked at the drawing info label? Sometimes the correlation is there.

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A. Here is the correlation :
- one triangle symbol is between 1000- 500 micro-inches
- two triangles symbol between 250- 125 micro-inches
- three triangles symbol is between 63- 16 micro-inches
- four triangles symbol is between 8- 0.5 micro-inches.

A.
1 Triangle = 250 µ inch = N9 = 6.3 µ meters to 500 µ inch = N10=12.5 µ meters
2 Triangles= 63 µ inch = N7 = 1.6 µ meters to 125 µ inch = N8 = 3.2 µ meters
3 Triangles= 8 µ inch = N4 = 0.2 µ meters to 32 µ inch = N6 = 0.8 µ meters
4 Triangles= <1 µ inch = N1 = 0.025 µ meters to 4 µ inch = N3 = 0.1 µ meters

A. Hi, Rahul.

Based on Guillermo's, Baudouin's, and Isaac's replies, it seems that this question will be hard to answer. But tell us the material of construction and the type of parts so we can at least give it a try. Thanks.

Regards,