Pipe cap

Fittings are used in pipe and plumbing systems to connect straight  pipe or tubing sections, to adapt to different sizes or shapes, and to regulate fluid flow, for example. Fittings, especially noncommmon types, can be expensive, and require time, materials, and tools to install, so they are a non-trivial part of piping and plumbing systems.  Valves are technically fittings, but are usually discussed separately.
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