The bearings are made the same size and shape as the contacts illustrated in Fig. 72, with the exception that a 1/8-inch hole is bored through near the top so that a small bolt may be slipped in to hold the knife blades in place.
The base of the switch measures 8 x 9 x 3/4 inches. The parts are assembled as in Fig. 71.
Another type of aerial switch called a "T" switch is illustrated in the same figure. A piece of 3/4-inch hard rubber is sawed in the shape of a T, 3 1/2 inches high and 6 1/2 inches wide at the top. The upper contacts are mounted on arms of the "T" and connected to binding posts placed immediately above them, A slot, 1/2 inch wide and 3 inches long, sawed in the center of the leg of the T, permits the middle knife blade to move without obstruction.
[Illustration: Fig. 75. "T" Aerial Switch.]
A double pole, double throw switch may be easily adapted to form a "T" switch. Two knives are cut from sheet brass, of the same shape as those already on the switch but twice as long. The contacts at one end of the porcelain base are removed and the bearings of the knife blade fastened there in their stead. This forms a single throw, double pole switch having knife blades twice the length of the original double pole, double throw switch. A "T" shaped support for the upper contacts may be sawed out of 1/2-inch hard rubber and smoothed up with a file. The support is fastened upright by means of two screws which pass through holes in the center of the base where the knife bearings originally were. The two contacts which were removed from the base are fastened to the support directly over the knife blades so that they make a good contact when the switch is up. Two binding posts mounted above the contacts make connection with them.
If desirable the switch may be fitted with a third knife blade and contact so that when the switch is up in position for receiving, the primary circuit of the induction coil or small transformer is open.
It is obvious that the dimensions, etc., need not be the same as those given here but may be adapted to suit the size and design of the switch which is to be altered. The knives should always be as long as convenient and the contacts separated by a wide space.