Which one of these is not a type of hole you can create?

The option that does not represent a type of hole is external threads. In the context of hole types, blind holes, counterbore holes, and through holes refer specifically to the different methods and characteristics of creating openings in materials.

A blind hole is one that does not go all the way through the material, having a bottom surface, whereas a through hole extends from one side of the material to the other, creating an opening that fully penetrates the workpiece. A counterbore hole is characterized by its cylindrical recess that allows the head of a fastener to sit below the surface of the material.

On the other hand, external threads refer to the feature on the outer surface of a cylindrical object, such as a bolt or screw, but they do not describe a type of hole. Instead, they involve the formation of a helical ridge around the cylinder which allows it to be fastened into a corresponding internally threaded hole. Thus, while external threads play a crucial role in fastening applications, they do not fit into the category of hole types.