Datum
The datum line is a base line parallel to the plane of the underbody or the frame where all vertical measurements originate. A datum line is an imaginary horizontal plane that runs below and runs parallel to the vehicle. The height dimensions are calculated at right angles from the datum to a given a control or a reference point on the underbody.
The height dimensions determine the location of the datum based on the equipment being used. Different datum lines are established for the same vehicle. You can add or subtract an equal amount from all height dimensions and create a new datum line for your usage. Refer to Collision Repair for datum line dimension.
Centerline
A centerline is an imaginary vertical plane that is perpendicular to the length of the datum plane through the center of the vehicle. The centerline is any line drawn through the center of the vehicles datum plane.
Form and Pierce
Form and pierce is a manufacturing process that forms an area in the metal structure to a desired three-dimensional measurement. The area is pierced with a hole or slot for dimensional gauging and may also be used for structural attachment of component pieces.
All measurements are read from a formed surface and the centerline of the hole.
All Dimensions are measured from:
| • | A length to the Zero Line. (1) |
| • | A height to Datum Line. (2) |
| • | A width to Center Line. (3) |
All dimensions are symmetrical unless otherwise specified.
Refer to measurement identification table for hole identification.
