These countersinks are well made to withstand heavy use. Each has a high-speed steel drill bit with slow spiral fluting for quick, clean cuts and a carbide-tipped countersink for exceptional wear resistance.
The depth stop has a free-spinning, low-friction collar to prevent surface marring and large side openings for chip clearance. You can adjust the depth of the pilot hole and the countersink/counterbore independently.
The 1/4" hex shank is grooved for use with quick-change chucks. Two sizes are available, designed for use with #8 and #10 screws. The #8 unit has a 1/8" drill bit and 3/8" diameter countersink, while the #10 has a 9/64" bit and 1/2" countersink.