13.3.2.1-3 Distinguishing Noninterchangeable Modules

The appearance of noninterchangeable modules should be distinguishable, and the difference should be apparent when the module is in its installed position.

Additional Information:
Interchangeable units of equipment should be clearly identifiable and easily distinguishable from units that are similar, but not interchangeable. Identification methods might be physical (such as size, shape, and mounting provisions) or visual (such as color coding and labeling).