Connectors
Connectors or fittings are used to join conduit to switch boxes, isolator boxes, electric motors and so on. This is usually done by pushing the connector thread through a pre-punched hole in the box called a knock-out and tightening with a locknut.

On some installations such as hazardous areas, the equipment is more robust and the hole for the cables already has a thread i.e. threaded entry.  This allows the connector to be screwed straight in, without the need for a locknut.

Occasionally connectors join two ends of conduit (usually for long runs or when the customer under-orders on conduit length).  This is bad practice but can be done by screwing two connectors into a threaded coupler, not forgetting to seal the threads.

Compression connectors or fittings
Compression fittings squeeze or hang-on to the outside of its conduit like "C" types.  These versions can be used for insulated systems.  Insulated systems make sure that when conduit and cables become damaged, the equipment and you do not become "live".

The opposite of an insulated system is an earthing system.  This has metal contact from the core through the connector and down to "earth".  When a fault occurs, stray electricity is directed away for safety.  In pliable systems the metal core is exposed to make the necessary contact inside the connector body. This is the principle used for screening where a combination of connector and fitting will protect sensitive computer cables from foreign signals and interference by conducting them down to Earth.

Screw-In connectors or fittings
Connectors for steel flexible conduits generally screw directly into the metal core which provides the earth path as well as giving a high pull-off load.  Conduits must not be used for Earthing and a separate earth wire must be run inside or outside the conduits.

Connector materials
Connector materials vary, partly because of where they are used, but largely depending on how they are made.  Most are machined from steel bars which are strong but have to be plated in zinc, nickel etc. to stop corrosion.

Angled connectors, because of their awkward shape, have to be cast in malleable iron.  Like steel these are usually protected by coating in zinc.

All plastic parts, sleeves, claws seals and throat insulators, etc, are moulded.  This permits smooth intricate shapes to be produced.