Set-squares are invariably used in connection with the tee-square, as
shown in fig. 148. The illustrations below show several patterns of the
device; by these, vertical lines, triangles, squares and hexagonal,
octagonal and twelve-sided figures, diagonal section lines, etc., can be
easily drawn. For ordinary purposes, a triangle or set-square with
angles of 45° may be 4 inches long and the other 8 inches in length, but
a six-inch set-square having angles 90°, 45° and 45°, and an eight-inch
one having angles of 90°, 60° and 30°, will be found sufficient for all
purposes; there are other triangles used specially for making letters.
[Illustration: Fig. 153.--Fig. 154.--Fig. 155.--Fig. 156.]
In practice the triangles or set-squares are slid along the edge of the
blade, and need not be any thicker than it.