The pipe used in Durham work is galvanized extra heavy, or standard wrought-iron, or steel pipe. It is almost impossible to recognize wrought-iron from steel pipe without the aid of a chemical or a magnifying glass. To test the pipe to distinguish its base, take a sharp file and file through the surface of the pipe that is to be tested. If the pipe is steel, under a magnifying glass the texture of the filed surface will appear to be smooth and have small irregular-shaped grains, and there will also be an appearance of compactness. If the pipe is iron, the texture will have the appearance of being ragged and will show streaks of slag or black. When screw pipe is cut there is always left a large burr on the inside of the pipe. This burr greatly reduces the bore of the pipe and is a source of stoppage in waste pipes. After the pipe is cut this burr should be reamed out thoroughly. One of the strong points of screw pipe is the strength of each joint. Care should therefore be taken to see that perfect threads are cut on the pipe and that the threads of the fittings are perfect. The dies should be set right and not varied on each joint. There should be plenty of oil used when threads are cut so that the thread will be clean and sharp. The follower or guide on stocks should be the same size as the pipe that is being threaded, otherwise a crooked thread will result. If a pipe-threading machine is used, the pipe is set squarely between the jaws of the vise that holds the pipe in place. When cutting a thread on a long length of pipe, the end sticking out from the machine must be supported firmly so that no strain will come on the machine as the pipe turns. It is necessary to cut crooked threads sometimes on the pipe to allow the pipe pitch for drainage or to bring the pipe into alignment where fitting would take up too much room. To cut a crooked thread on a piece of pipe, simply leave the follower out of the stock or put in the size larger. The dies not having a guide will cut a crooked thread. Piping should be run with as few threads as possible. With a thorough knowledge of and the intelligent use of fittings, a minimum number of threads will result.

The pipes in a building are run in compact parallel lines in chases designed especially for them. The tendency is to confine the pipes to certain localities as much as possible. This makes a very neat job and in case repairs are needed, the work and trouble incurred will be confined to one section.