As is true to all manual tools, pliers are made to increase the effectiveness of human hand.
Pliers are designed according to the principle of the two-armed lever which makes it possible to convert lower force (e.g. manual force on the shanks of the pliers) into a greater force which in the case of pliers is effective in the gripping jaws or in the cutting edge.
The force in the jaws which produces a gripping type of movement when the shanks are pressed together increases with the leverage ratio. In the case of a pair of pliers with which large forces are to be produced, the distance from the centre of the rivet to the handle must be large and the distance from the rivet centre to the gripping jaws or cutting edge must be as small as possible.
Many pliers however do not so much increase manual force as they make it easier to work in awkward places, e.g. in the assembly of electrical appliances and in electronics and precision engineering.
The origin of the pliers in Europe goes back to about the second millenium before Christ, that is to a time in which people began to forge iron. The pliers made it possible to grip red-hot iron and hold it when forging on the anvil. The shape of the forging pliers used then has remained up to the present day with hardly any alteration.
The number of types of pliers grew with the expansion of crafts and trades and later industrialisation. At present, there are about 100 different commonly used types of pliers. The number of special versions for very specific applications is growing constantly. Of course, such special versions are often not commercially available.
In Germany alone over 1 million pliers are produced each month and of these about 50 % are exported. The most common types of pliers are for example side cutters, combination pliers and water pump pliers.
As a fundamental principle a differentiation is made between:
A pair of pliers consists of three parts:
With respect to the joint construction a distinction is made between:
Pliers are forged out of alloyed and unalloyed tool steel. For simple pliers unalloyed tool steel with a carbon content of 0.45 % is used. Top-quality and heavy-duty pliers are made out of materials with a higher carbon content and/or alloying elements such as chrome or vanadium.