What factor is used to differentiate between dimpled and countersunk materials?

The factor that is used to differentiate between dimpled and countersunk materials is thickness. This is because the design and engineering of these features are closely related to the thickness of the material.

In aircraft structures, countersinking involves creating a conical hole that allows the head of a fastener to sit flush with or below the surface of the metal. This process is often applicable to thicker materials, where a deeper cavity can accommodate the necessary fastener head without compromising structural integrity.

On the other hand, dimpled materials feature a slight indentation rather than a deeper conical hole. Dimpling is generally used for thinner materials to maintain the structural strength while reducing aerodynamic drag. Since dimpled profiles do not require as much material removal as countersinking, they are more suitable for lighter weight applications in thinner sheets.

Thus, the distinction between these two methods is primarily based on the thickness of the material being worked with, as it dictates the appropriate fastener installation technique and the resulting structural properties.