Plugs & Caps
Caps and plugs, usually liquid- or gas-tight, cover the end of a pipe. A cap attaches to the male thread of a pipe. It may have a solvent-weld socket end or a female-threaded end. In threaded plumbing systems, the cap has female threads. Industrial caps may be round, square, rectangular, U- or I-shaped, and may have a handgrip. If a solvent-weld cap is used to provide for a future connection point, several inches of pipe must be left before the cap; when the cap is cut off for the future connection, enough pipe must remain to allow a new fitting to be glued onto it.
A plug fits inside the fitting to which it is mated. In a threaded plumbing system, plugs have male threads. There are a number of plug types: mechanical, pneumatic-disk, single-size pneumatic rubber, multi-size pneumatic and flow-through, and high-pressure.