A great number of rods with circular ends are joined to their respective portions by means of sockets or socket-ends. A socket-end is a tubular boss or projection situated at one end, or both ends, of an article, and usually in one piece with it. A socket is always furnished with a hole of some shape, and, although a few socket-holes are square, the greater number are circular, and are either straight simple holes slightly tapered, or holes that are screwed.

Ends of slide-rods, piston-rods, pump-rods, and others, are frequently fitted with socket-ends, and are represented by Figs. 966, 967, 968, and 969. These denote the ordinary classes of sockets, some being fastened together by screws, and others by keys. Those fastened with keys are the easiest to connect and disconnect; but it may be said generally that the screwed ends are preferable for obtaining a maximum strength with a minimum amount of metal, supposing that the thread-grooves of the respective parts are not deeper than is needful. The author's plan is to furnish all such screwed ends with threads having comparative short steps.

The ends of rods and bars to be entered and fixed in sockets require to have special bearing surfaces, if to be fastened with keys, that the keys may effectually tighten the respective pieces together without exerting any improper strain. Supposing that an end of a piston-rod is to be thus connected, its principal bearing surface is at the bottom of the hole. In Fig. 968 a cross-head boss is shown, in the hole of which is a rod's end. This end is of a regular curved form, and accurately fits the hole's bottom; consequently, the hole must have been previously carefully bored to its proper shape, a suitable bearing of this character being required because the rod cannot be furnished with a flange for contact around the hole's mouth.

The necessity for making a piston-rod's end, or a slide-rod's end, bear in close contact with the bottom of the hole, arises from the small amount of bearing-surface presented by the shoulder of the rod at the mouth of the hole. Such a comparative small surface soon gets out of shape by the action of the rod; and an irregular recess is also formed into the metal of the boss at the hole's mouth. This necessitates a frequent driving in of the key, to tighten the rod, although such fastening is not effectual for any considerable time. An end of a rod that does not touch the bottom, is also liable to be weakened by the act of keying the parts together. It may, therefore, be seen that a proper bearing must be provided either at the bottom of the hole or at its entrance.

An end of a connecting-rod, or of an eccentric-rod, can have a flange, similar to that seen in Fig. 969; and the rod's end can be screwed and the flange made to bear tight upon the boss by the act of screwing the end into the hole. The fastening may be also effected by means of a key, the end of the rod being fitted into merely a plain hole. An eccentric-rod attached in this manner is shown by Fig. 970, the flange or collar being tightly forced against the face of the boss while driving the key into its key-way.

In some cases an end is both keyed and screwed; but keying is quite unnecessary if the screw-cutting is properly done.