The marked part of the bit is used to start the hole. The spur is
made like a screw, which pulls the bit into the wood as you turn the
bit. The parts marked lip and nib are the cutting parts. The twist
portion removes the shavings from the hole. The shank ends in a
tang, which fits into the brace.
(2) Expansion Auger Bit. An expansion bit (Figure 22) is used
to bore a hole larger than 1 inch, such as for a door lock. Notice
that the cutting bit has a scale for adjusting the size of the hole
needed. The screw shown is used to lock the cutting blade into
position. The screw must be tightened to keep the blade from moving
and changing the size of the hole. This bit also has a tang to fit
into the hand brace.
Expansion auger bit
(3) Twist Drill. A twist drill is used to make holes in wood,
metal, fiber, plastic, and other materials. Carpenters often drill
holes in metal to which some type of wood or fiber will be bolted.
This requires the use of a special type of twist drill (Figure 23).
Twist drill bits are driven by electric or hand drills (Figure 24).