When the motion between a pair is limited to a definite direction irrespective of the direction of force applied, then the motion is said to be a completely constrained motion.

Fluid link is a link which has a fluid in the receptacle and the motion is transmitted through the fluid by pressure or compression. Example for Fluid Link are Hydraulic Crane, Jack, Brake, etc.

Single slider crank chain is a modification of the four bar chain. Single slider crank chain consists of one sliding pair and three turning pairs. It is, usually, found in reciprocating steam engine mechanism. This type of mechanism converts rotary motion into reciprocating motion. The inversions of a single slider crank chain are found in the following mechanisms.
* Pendulum pump or Bull engine
* Oscillating cylinder engine
* Rotary internal combustion engine or Gnome engine.
* Crank and slotted lever quick return motion mechanism.
* Whitworth quick return motion mechanism.