Conduit

Electrical Conduit Tubing
Conduit fitting, externally threaded, multipart compression fitting with elastomaric seal. Stainless steel body and nut and nickel plated brass insert.
An electrical conduit is a tube used to protect and route electrical wiring in a building or nonbuilding structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purposes. Conduit is generally installed by electricians at the site of installation of electrical equipment