A parallel constraint forces two lines to remain parallel to each other.
In the example below, a parallel constraint has been applied to the two lines on the left. The result is the block definition on the right, where the lines are parallel to each other.
Manipulate a Parallel Constraint
When you manipulate a block with a parallel constraint applied, the specified lines will always remain parallel to each other.
In the example below, a parallel constraint has been applied to one line in each of the rectangles on top. The geometry of each rectangle on the bottom has been changed, but the constrained lines remain parallel to each other.