To ensure that after manufacturing a surface has a certain distance between two parallel planes, the symbol Flatness is used.
The distance is entered after the symbol.
Flatness is a shape tolerance and describes in which range the most protruding and the most curved area of a surface may be apart.

Flatness in Injection Molding

Quality Assurance: Symbol of tolerated property with 0.06mm required flatness

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.