Fig. 1452.
For larger work we have the compasses, a common form of which is shown in [Fig. 1452], in which the leg a is slotted to receive the arc piece c, which has a threaded stem passing through e, and is provided with a nut at b; at d is a spring which holds the face of the nut b firmly against the leg e; at a is a thumb-screw for securing the leg to the arm c. The thumb-screw a being loosened, the compass legs may be rudely adjusted for distance apart, and a is then tightened. The adjustment is finally made by operating the nut b, which, on account of its fine thread, enables a very fine adjustment to be easily made.
Fig. 1453.
It is often very convenient to be able to set one leg of a pair of dividers to be longer than the other, for which purpose a socket b, [Fig. 1453], is provided, being pierced to receive a movable piece a, and split so that by means of a set-screw c the movable piece a may be gripped or released at pleasure.
