Counterboring
Counterboring produces cylindrical recesses in holes, widening the hole to a limited depth.
Counterboring provides a simple way to recess conventional or socket head screw heads but can be used for any other purpose.
Counterboring can be done in almost any hard material. Tooling used in counterboring are usual stock items.
The process of counterboring is often done on CNC milling machines, lathes and drill presses.