or also called line profile, is a form tolerance and describes a tolerance zone which is limited by two curves (envelope lines or envelope curves).
This tolerance defines how the curvature of a part must be designed.
The measured profile line must lie at every point across the thickness of the molded part between the envelope lines running at the given distance.
The distance between the two equidistant enveloping lines is formed by circles with the specified diameter.
The centers of the circles lie on the shape specified as geometrically ideal.

Profile of a line in Injection Molding

Quality assurance: Profile shape line tolerance with enveloping lines at the distance of a circle diameter of 0.09mm

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