3" body 120° countersink, 3 flutes.
A countersink cuts the tapered seat that lets a flat-head screw finish flush with the surface. This one has a 3" cutting body on a 1" shank, 5" overall, ground to a 120° included angle.
The "chatterless" grind stays in contact with the work rather than skipping across it, which is what stops the tool from cutting a lobed, faceted hole.
A 120° included angle gives a wide, shallow chamfer — often used to break an edge or to prepare a hole for a weld.
