This is an instrument in the form of a letter T, as shown in the figures
149 and 150; the two parts are known as _stock_ and _blade_; the
horizontal part of the letter (T) is the stock, and the vertical part
the blade--hence the name, T-square; to form the square, the two parts
are joined together in such a way as to make them exactly at right
angles to each other; the stock, which is applied to the working edge of
the drawing board, being about one-third the length of the blade, and
about three times its thickness.
[Illustration: Figs. 149 and 150.]
To be perfect in construction, a tee-square should be as light as is
consistent with its necessary strength and stiffness of parts; it should
be made of suitable material easily manufactured, put together, and
repaired, and withal as truly correct as is possible to be made. Such a
square is represented in fig. 148; it has a taper blade, which is
generally about double the width where secured to the stock as it is at
the end.
[Illustration: Figs. 151 and 152.]
The manner in which the stock is united to the blade determines its
adaptability or otherwise to the use made of it; in some the stock is
rectangular in section, and the blade mortised into it; in others the
blade is dovetailed and let into the stock for the whole of its
thickness.