────────────────────────────────────────────────────────────────── Size of Coil Length of Tube Diameter of Tube ────────────────────────────────────────────────────────────────── 1/4 inch 4 1/4 inch 2 1/2 inch ────────────────────────────────────────────────────────────────── 1/2 inch 4 1/2 inch 2 1/2 inch ────────────────────────────────────────────────────────────────── 1 inch 6 1/2 inch 3 inch ────────────────────────────────────────────────────────────────── *The Spring* is a piece of thin steel, three-eighths of an inch wide and two and one-eighth inches long. Several holes are drilled in it. The illustration shows the exact location of these holes. The holes A and C should be just large enough to allow an 8-32 machine screw to slip through. The hole B is just large enough to receive a piece of contact wire. *The Contact* wire should be about three-thirty-seconds of an inch long and be slipped in the hole and riveted in place. *The Armature* is a piece of soft iron cut out of a rod one-half an inch in diameter. It should be about one-quarter of an inch thick, but should have a small stud left on one face so that the stud may be slipped into the hole marked C in the steel spring and the armature then riveted firmly to the spring by flattening out the stud. [Illustration: FIG. 117.—The Bridge.] ────────────────────────────────────────────────────────────────── Size of Coil E Length I Width ────────────────────────────────────────────────────────────────── 1/4 inch 4 7/8 inch 3/4 inch ────────────────────────────────────────────────────────────────── 1/2 inch 5 1/8 inch 3/4 inch ────────────────────────────────────────────────────────────────── 1 inch 7 1/8 inch 3/4 inch ────────────────────────────────────────────────────────────────── The spring is bent at right angles about one-half inch from the end as shown by the dotted line in Figure 115. *A Cardboard Tube*, two and one-half inches in diameter and four and one-quarter inches long, is used to inclose the primary and secondary windings when they are in position. The tube may be given a very fine appearance by gluing a single layer of black bookbinders’ cloth over it. *The Bridge* shown in Figure 117 is a strip of wood about one-eighth of an inch thick, four and seven-eighths inches long and three-quarters of an inch wide. It is stained to match the base and is then given a coat of shellac or varnish. Two holes are bored in, the bridge, one inch from each end. The coil is now ready for assembling. Figure 118. shows a cross-section of the complete coil.