[Illustration: FIG. 69.--Cross-section of plain compression bibb-cock for a solder joint.] Fig. 69 shows quite clearly the mechanical arrangement of the compression cock. When the handle is turned the nut _C_ lifts the valve from its seat _B_, allowing the water to escape. The piece _D_ is generally made of composition rubber that may be bought at the dealers for a trifling amount but it may be replaced temporarily with a piece of leather. The part _E_ is packing, to keep the water from leaking out around the stem. The packing may be obtained from the dealer especially for the purpose or it may be made of a disc of sheet rubber. In fact, anything that can be put into the space will answer the purpose temporarily. The valve is closed by compression, hence the name compression cock. All cocks made to open and close in the same manner are compression cocks. [Illustration: FIG. 70.--Cross-section of plain self-closing bibb-cock for lead pipe.] [Illustration: FIG. 71.--Cross-section of lever handle, plain bibb.] [Illustration: FIG. 72.--Cross-section of plain Fuller bibb for lead pipe.] =Self-closing Bibbs.=--In Fig. 70 is one example of the many styles of self-closing bibb-cocks. When the handle of this cock is turned, the steep-pitched screw _A_ opens the valve and at the same time compresses the spiral spring _B_, when the handle is released, the valve is pressed back on its seat by the spring. Self-closing cocks are used to prevent the waste of water at drinking fountains, wash basins and other places where the water is apt to be left running through carelessness. =Lever-handle Bibbs.=--Fig. 71 is an example of the _lever-handle_, _ground-key_ bibb-cock. The key is the piece _A_, which is tapered and forms a ground joint with the part _B_. The cock takes its name from the form of the handle. The term ground-key means that the key has been ground into place with emery dust. This cock is kept from leaking by adjustment of the screw _C_.