Electrical Metallic Tubing
Unthreaded, circular cross-section. It always used for protecting wires and cables.

EMT Conduit is a metal thin walled conduit that comes in ten foot lengths. 

These sticks have no couplings on the ends.
Couplings and connectors can be added to connect the next piece. 

These couplings come in set screw and compression types.
Set screw couplings have two screws, one for each piece of conduit which holds the conduits together and also bonds the ground connection between the conduits.


Advantages:

Steel Thin wall EMT conduit is easy to cut and easy to bend - reducing waste and installation time.
Metal conduit is non-combustible and easily adaptable to future wiring changes.
Metal conduit is a proven equipment grounding conductor and can reduce electromagnetic fields by up to 95%.