SPRING BOWS.
These were originally developed from the common form of compasses, with a single spring leg; later, the demand for smaller sizes made changes necessary, and spring bows are now made symmetrical, both sides of the bow being made to “spring.”
[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.