Counterbore
Counterbores are rotary cutting tools with a pilot tip to guide cutting lips into the hole. They are used to form a recess for a capscrew head or to enlarge a hole without changing its relative position. They are available in a variety of styles and sizes for specific applications.
FILISTER HEAD SCREW COUNTERBORES
Filister Head Screw Counterbores page 180A
Filister Head Screw Counterbores are designed to create a recess for small fillister and flat head machine screws. Solid pilot will not score or damage pilot hole. Cutting action is chatterless.
CAP SCREW COUNTERBORES
Cap Screw Counterbores page 182 360° view
Cap Screw Counterbores are designed to create a recess for socket head cap screws and shoulder screws.  They are also used for spot facing smaller spots, enlarging, or cleaning holes.  Solid pilot will not score or damage pilot hole.  Cutting action is chatterless.
Cap Screw Counterbores - Metric page 182
Metric Cap Screw Counterbores are designed to create a recess for socket head cap screws and shoulder screws. They are also used for spot facing smaller spots, enlarging, or cleaning holes. Solid pilot will not score or damage pilot hole. Cutting action is chatterless.
INTERCHANGEABLE COUNTERBORES
Short Series Interchangeable Counterbores - High Speed Steel page 180
High Speed Steel Short Series Interchangeable Counterbores are used to create a recess for a cap screw, spring, or bolt. They are used with interchangeable pilots ground to fit various hole sizes to be counterbored.
INTERCHANGEABLE COUNTERBORE PILOTS
Interchangeable Counterbore Pilots - Carbon Steel page 181
Carbon Steel Interchangeable Counterbore Pilots are used with interchangeable pilot style counterbores and spot facers, including carbide tipped and aircraft counterbores to produce various combinations of sizes. All counterbore pilots have flat on one side of shank. To order, select a pilot with a shank diameter to fit the pilot hole diameter of the counterbore being used.