These are exceptionally smooth high-carbon steel countersinks.
Used after pre-drilling for a screw, they cut cleanly and are chatter-free. The cone tip assures accurate centering and the cutter design ejects chips rapidly. They can also be used for counterboring as necessary.
Available in two sizes: 3/8" dia. (1/4" shank) and 1/2" dia. (5/16" shank). 82° countersink.