In rough carpentry, after drilling a hole for a woodscrew, a bit with taper similar to that of
the head of the screw is used to enlarge the top of the drill hole, so that when the screw
is tightened, the top of the screw will be flush with the surface of the work. Also when I
worked in foundry machine shop, castings for school seats had to have tapered holes
for head of screws that fastened them to the floor were cast slightly undersized, and had to
be reamed out so screw heads were flush with the surface of the base of the casting.