In general, the mechanical fastening elements have the function of providing controlled communication in the power transmission line between the rotating element and the rotating element in a machine. Connection elements are generally referred to as couplings. The main tasks of the couplings are as follows: connecting and separating shafts, transmitting forces and moments, eliminating unevenness between shaft axes and damping shocks and vibrations.

While performing these tasks, the coupling is realized by mechanical bonding. Therefore, in order to ensure or disconnect the two shafts, the mechanical fastener must be installed and removed without any movement of the shaft.

The most important factor for couplings is the unevenness between the shaft axes during assembly or operation. These irregularities consist of deviations between shaft axes due to mounting errors or thermal elongations and are radial, axial, angular and torsional. Furthermore, another important element for couplings is that the axes of the two shafts to be connected to each other are in the same direction.

In general, the shafts used between the engine and the propeller on ships, the shafts used in the moving systems of the bridge cranes and the long shafts used in some textile machines have coupling type mechanical couplings.

Another example of mechanical fasteners are couplings. In clutches, the contact can be both mechanical and may depend on a physical event, ie friction. The clutches are mainly divided into five groups: mechanical clutches, pneumomechanical clutches, electromechanical clutches, electromagnetic clutches and automatic clutches.

The working principle of the couplings is based on the connection of one side to the fixed rotating shaft and the other side to the rotating shaft. There is no slippage between the contact surfaces and both shafts rotate at the same speed.

Mechanical connection tests carried out in advanced laboratories comply with the methods and standards published by domestic and foreign organizations.