3" body 90° 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 90° 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.
90° is the standard included angle for metric flat-head screws, and the common choice for chamfering a hole before tapping.
