What is the primary purpose of a counterbore?

The primary purpose of a counterbore is to create a flat-bottomed hole. This machining process involves using a counterbore tool that has a specific design to not only increase the diameter of the existing hole but also to produce a flat bottom. This flat-bottomed feature is crucial for applications where a screw head or a bolt needs to sit flush with the surface of the material, ensuring a clean finish and proper engagement with the fastener.

The design allows for precise depth control, which is important in applications such as assembly work, where maintaining a specific elevation is essential. This differentiates counterboring from drilling or simply enlarging a hole, as the latter does not necessarily result in a flat-bottomed profile.