// is the GD&T symbol for parallelism. For the parallelism symbol, notice how the two lines of the symbol run together. They are parallel to each other.
How to read a parallelism blueprint callout
The blueprint item that contains the parallelism callout is called a feature control frame.
The components of a feature control frame are shown below.
The parallelism symbol would be inside the first box to indicate the type of tolerance.
The tolerance amount is listed in the middle box. This tolerance is in the the same units that the rest of your blueprint is in. Many times this will be listed in general tolerance block of the blueprint.
The datum reference is the feature that the feature with the parallelism callout will be compared to. In the example below, datum A is on the left and the right side has the parallelism callout attached to it.
This feature control frame reads “the right side of the part must be parallel within 0.02 to datum A”.