Pipes and fittings are the component parts of plumbing systems. Metal or plastic pipes are connected by  various fittings planned to conjoin lengths in a straight line, rotate corners, enlarge or reduce pipe size, ramify in two directions or connect to a certain type of fixture.
More than a few different metals and plastics are applied for pipes manufacture. It is possible to classify a pipe according to its makeup and size: indoor water-supplies typically are copper or galvanized iron pipe in diameters of 1/2 inch, 3/4 inch or 1 inch; some water-services in these diameters are made of plastic pipe. Gas-transmission pipeline has similar size, but is generally made of galvanized iron or black (uncoated) pipe.
Water feed that supply ice makers, hot-water dispensers, water filters and all that exploit smaller-diameter, plastic or flexible copper tubing. Fittings may be made of brass or plastic. Also you can find flexible (at times ribbed) pipes serving from a small wall valve to toilets and faucets and flexible piping designed for carrying gas from valves to dryers, water heaters and other gas appliances.
Drain, waste and vent (DWV) piping deal with larger-diameter pipes, from 1 1/2 inches to 4 inches. A 4-inch or larger plastic or cast-iron pipe commonly serves the main drain passage, the waste and venting line that serves lavatory basins and other bathroom fixtures. Other venting and waste lines are usually supplied with pipes having 1 1/2 inches and larger size in diameter; sometimes light-gauge plastic pipe from 1 1/4-inch to 1 1/2-inch diameter is used for integrated vacuum cleaning systems.
Various plumbing applications make use of plastic pipe, probably for the reason that it has moderate price, easy to set up and corrosion resistant. Nonetheless, in some locations plastic pipe is prohibited by codes for supply pipeline.
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