Head, twist, and shank are ground after hardening. Shank is same diameter as drill. Left 8.58 Pic. For boring tapered holes for wood screws.
Twist is tapered to correspond to threaded portion of screw.
Shank is same diameter as drill. Works will in applications where countersink and center drill diameters are too close for a standard configuration. 28 Popular for cross-grain boring and other general work requiring smooth, accurate holes. Head, twist and shank are ground after hardening. Shank is same diameter as drill.