Ratchet-Brace.] For heavy work, screwdriver-bits, Fig.

189, in a bit-stock are useful, and for quick work, the spiral screwdriver, Fig.

190, and for small work, the ratchet-screwdriver.
7.

MEASURING AND MARKING TOOLS.
It is a long step from the time when one inch meant the width of the thumb, and one foot meant the length of the foot, to the measuring of distances and of angles which vary almost infinitesimally.

No such accuracy is necessary in measuring wood as in measuring metal, but still there is a considerable variety of tools for this purpose.
[Illustration: Fig.186.Inserting a Bit in Stock.] [Illustration: Fig.187.