Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3?8 inch (9.5 mm) to 2 inches (51 mm).It is rarely used today for new construction residential plumbing. Steel pipe has National Pipe Thread (NPT) standard tapered male threads, which connect with female tapered threads on elbows, tees, couplers, valves, and other fittings.
Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas. Źródło: https://en.wikipedia.org/wiki/Plumbing
An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made.The ends may be machined for butt welding, threaded (usually female), or socketed, etc.When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow. Elbows are categorized based on various design features as below: Long Radius (LR) Elbows ? radius is 1.5 times the pipe diameter Short Radius (SR) Elbows ? radius is 1.0 times the pipe diameter 90 Degree Elbow ? where change in direction required is 90° 60 Degree Elbow ? where change in direction required is 60° 45 Degree Elbow ? where change in direction required is 45° A 90 degree elbow is also called a "90 bend" or "90 ell".
It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe.
It is used to change the direction in piping and is also sometimes called a "quarter bend".
A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead.It can also attach to rubber with stainless steel clamps.It is available in many materials like silicone, rubber compounds, galvanized steel, etc. The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains. These elbows can be made from tough nylon material or NPT thread.Źródło: https://en.wikipedia.org/wiki/Piping_and_plumbing_fitting
All such work can be carried out also by plumbers self-employed.