What type of hole is indicated by the label A in the diagram?

The label indicating a countersink hole refers to a hole that has been conically shaped at the top, allowing for the installation of fasteners such as screws to sit flush with or below the surface of the material. This feature is particularly important in applications where a smooth surface is desired, both for aesthetic purposes and to prevent snagging. In the manufacturing and machining processes, countersinking aids in creating a clean finish and can also contribute to the strength of the assembly by helping to distribute the load on the fastener.

Countersink holes are typically specified with a certain diameter and angle, often used to accommodate specific types of screws or bolts. Recognizing this feature in diagrams is crucial for anyone working in design, engineering, or assembly, as it impacts how components interact and function together.

The other types of holes listed have different characteristics: drilled holes are simply created to remove material without any special shaping, tapped holes have internal threads designed to accept screw threads, and blind holes are drilled to a specific depth but do not go all the way through the material. Each of these serves unique purposes in various applications, but they do not provide the specific conical shaping that characterizes a countersink hole.