Counterbored holes are cylindrical holes that are drilled into the surface of a PCB board. These holes are specifically designed to accommodate screw caps, providing a recessed space for the screw head to be flush with the PCB surface. The counterboring drilling method is used to create these holes, utilizing drills with two different cutting diameters to ensure an even surface on the inside wall of the hole. Counterbored holes are typically used for standard screw cap fixes and are relatively simple to drill due to their straight, vertical nature. However, it is important to note that counterbored holes have limited flexibility in terms of sizing or variation. They are specifically tailored to fit hex-headed screws and are not suitable for other types of fasteners.