A constant velocity joint is a disconnectable component which allows the transmission of rotary motion between two shafts (or other rotating elements) while maintaining the transmission ratio constantly at one to one.
In practice, the movement is transmitted uniformly without the oscillations in velocity typical of universal joints. Today, these joints are used more or less universally in order to connect drive-shafts to the steering wheels in cars with front-wheel drive.
There are various models of constant velocity joints, and they can all be categorised into two main groups: sliding joints and non-sliding joints!
The task of sliding joints is to allow the axle-shaft to modify its own length in order to follow the movement of the suspension, crucial in the event of an uneven road surface.