When attaching accessories or components, what part of a frame rail should not be drilled?

The flange of a frame rail should not be drilled when attaching accessories or components because it plays a critical structural role. The flange is designed to distribute loads and provide torsional strength to the frame. Drilling into the flange can compromise this strength, leading to potential failure in high-stress applications, such as during driving or in collision situations.

Maintaining the integrity of the flange is crucial for the overall performance and safety of the vehicle. Other parts of the frame rail may be more suited for modification, but the flange is specifically designed to remain intact to ensure proper load handling and structural integrity.