Connector/Coupling

Fittings and couplings are used to connect two parts, strips, rods, threaded rods

Connector

The connectors are used to join axes or rods they are simple or triples
Arm Crank

Crank arm can be single, double, tapped or not
Bell Crank

Bell Crank can be simple or hub according to the built model
Coupling

The couplings are used to join 2 axles rods, a rod and a strip, a rod and a threaded rod between other uses