28 ELEMENTARY WOODWORKING 
the wood, and so a smooth hole could be bored; but 
considerable pressure was necessary to force the tool 
through the wood. 
The progress that has been made in the manufacture 
of tools can be easily appreciated by comparing this 
center bit with the modern auger bit. 
Referring to the sketch (Fig. 38), BB are two knife 
points, or nibs, which cut the wood fibers before the 
chisel edges, or lips, C C, can touch 
the wood. The point A allows us 
to accurately place the center of 
Fic. 38. Details of the hole where we wish it, and the 
sa deed screw back of A draws the tool into 
the wood as it revolves. This part is known as the 
spur, or worm. On this class of bits no pressure is 
necessary. 
The opposite end of the bit, called the shank, fits into 
the brace. Any tool with such a shank, and designed 
for use with the brace, is a bit. We have screw-driver 
bits, gimlet bits, auger bits, etc. 
On the shank of an auger bit will be found a number. 
This is the numerator of a fraction whose denominator 
is 16. If we find this number to be 4, it is a 74g, or a 
t-nch bit. If the number is 16, we have a 18, or a 
one-inch bit, etc., always referring to the diameter of the 
hole which the tool will bore. 
