These tubes are made of the best rolled brass, one thirteenth of an inch thick, the edges of the brass are properly chamferred, and lapped over each other, and soldered together, the solder being applied inside; the tubes are then drawn through a circular steel die, to make them truly cylindrical. The holes to receive them in the tube plates e and n, are bored quite cylindrical, so as to fit the tubes exactly, which are just long enough to come to the outside of both plates; the ends of the tubes are then fixed by driving in a steel hoop or ferrule made slightly conical, as shown in Fig. 1, which is a section full size of the tube a a, the plate in which it is inserted, and the ferrules c c; the ferrule is a little larger than the tube, so that when driven in, it compresses the tube very forcibly against the sides of the hole, and makes the joint completely watertight. The ferrules are sometimes made of wrought-iron, but they generally do not last out the tube in that case, and require replacing by new ones before the tubes are worn out. The steel ferrules are better, as they last nearly twice as long.

When a tube or ferrule requires taking out, the ferrule is to be cut quite through with a chisel and then turned inwards, so as to detach it from the tube, which can then be driven out.