HValley Tools has a outstanding variety of countersinks and counterbores to meet your woodworking needs.
A countersink is an angled taper applied to a hole that allows a fastener (usually a flat head screw or similar) to sit even with, or below the surface which has been countersunk.
The counterbore bit is typically a specialized drill bit that creates the hole for the body of the fastener and the larger sized cavity for its head, both at the same time. Usually, the fastener is a flat-bottomed screw such as a round head or a pan head screw.
A pilot hole allows the screw threads to cut directly into the hole, which reduces the risk of splitting wood near an end or edge.