Which type of hole is designed for the head of a fastener to rest below the surface of a part?

The type of hole designed for the head of a fastener to rest below the surface of a part is a counterbored hole. This specific design allows for the head of a fastener, such as a bolt or screw, to sit flush with or beneath the surface of the material, providing a clean finish and preventing snagging or interference with other components. Counterboring increases the diameter of the hole at the top while maintaining a smaller diameter deeper down, creating a cylindrical shape that accommodates the fastener's head.

In contrast, a drilled hole is simply a hole created through material with a uniform diameter, which doesn’t provide space for a fastener head to rest below the surface. A countersunk hole, while designed to allow the head of a screw to sit below the surface, creates a conical shape rather than a flat cylinder, which is different from the cylindrical surface provided by a counterbore. A blind hole is a hole that does not go all the way through the material, which may or may not be used for fasteners, but it does not have the specific geometry required to accommodate the head of a fastener below the surface like a counterbored hole does.