the.com/countersink
the cone-shaped grave dug so a screw head can lie flush and dignified.
the angleMost are 82 or 90 degrees by standard
vs counterboreCounterbore is flat-bottomed; countersink is conical
chatter problemOdd flute counts reduce vibration marks in metal
naval rootsFlush rivets cut drag on aircraft and ships
double dutyAlso deburrs holes after drilling