In this case, a tolerance to be maintained is described by two parallel planes or straight lines.

These are spaced at the specified distance and are parallel to the specified reference.
A measured value must lie within these planes or straight lines.
For cylindrical moldings, the tolerance zone is formed by a cylinder with the diameter of the specified tolerance value.
The axis of the cylinder needs to be parallel to the reference.

Parallelism in Injection Molding

Quality assurance: The axis of the hole must be within a cylinder of 0.01mm.

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