[Fig. 182] are spring dividers.
[Fig. 183] is a spring pencil.
[Fig. 184] is a spring pen.
In these figures it will be seen that the two threads, a right and a left, are moved with one central thumbscrew; in the [figs. 185 to 187] a single screw is used.
In choosing spring bows, care must be exercised to select a sufficiently strong, stiff spring, as the relation between spring pressure and thumbscrew is important.
BEAM COMPASSES AND TRAMMELS.
In [fig. 188] is shown a set of beam compasses, together with a portion of the wooden rod or beam on which they are used.
Fig. 188.
The latter, as will be seen by the section drawn to one side, A, is in the shape of a T. This form has considerable strength and rigidity. Beam compasses are provided with extra points for pencil or ink work, as shown.