These old coils are really neat items to have around from a past era of amateur radio history among others. This one was manufactured by the K-W company. These coils were produced by many different companies including the Jefferson Electric Company.
The photograph on the left is of the points and vibrator section of the coil. The photograph on the right is of the top.
These coils were originally intended for items such as signs, automobiles, trains, toys, and anywhere a high tension spark was needed. Early one, two and four cylinder engines used these with batteries to provide ignition. These coils have also been used for the ignition of WWII flame throwers, roofing tar heaters, home heating plants, spark plug testers, fence chargers, railroad track cars, and of course radio spark gap transmitters. Other names for this item is buzz-coil and trembler coil.
The coil has three connecting points. One is for the power source which was usually a battery. The positive from the battery would be connected to this post. The second connecting point was for ground. The third connecting point was the output such as connection to a sparkplug. These coils also have an adjustment called a tension nut. The operator would turn the tension nut until the highest pitched tone was heard from the coil and upon doing so allowed the coil to produce the hottest spark possible.