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What Do Multiple Triangle Symbols in Surface texture notes mean?

Q. Surface texture symbol - I notice one to four triangles defining a surface finish. Can you tell me what this means expressed in micro inches, number or microns.


Sheldon Epstein
industrial ceramics - Houston, Texas


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.

Guillermo Marrufo
Monterrey, NL, Mexico

November 3, 2008

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.

Baudouin Matala
- Calgary (AB) Canada


July 20, 2012

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

Isaac Lin
- Folsom, California, USA

January 27, 2012

Q. Please tell me the process to gain triple triangle and four triangle surface finish

rahul wadhwa
- ambala, India

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.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey
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