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:
- cutting pliers to sever or pinch off (side cutters, front cutters, pinching pincers etc.),
- gripping pliers (flat pliers, long-jaw pliers, water pump pliers) and
- combined pliers, which are used both for severing and for gripping (combination pliers, stork beak pliers, radio pliers ect.).
A pair of pliers consists of three parts:
- the pair of handles by which the pliers is taken in the hand. The pair of handles should be designed in accordance with ergonomiv criteria, so that the pliers lie securely and comfortably in the hand;
- the joint, that is the pivot point of the pliers. The joint must move smoothly without any play so that the pliers can be opened and closed easily with one hand;
- the head with the gripping jaw or cutting edge. The head ends should be ground precisely to the right shape. The two cutting edges must be sharp and close on top of each other exactly to make it easy to cut wires with "spring".
With respect to the joint construction a distinction is made between:
- a lay-on joint, such as the pincers. the two halves of the pliers are placed on top of each other - without being milled out - and riveted.
- the lap joint, such as the combination pliers. Here one half of the pliers turns around the rivet but in a milled-out recess in the other shank.
- the box joint in which half of a pliers is pushed through a slit in the other half of the pliers. Box pliers - apart from water pump pliers - are very costly to produce and make it more difficult to use hard and alloyed steel. They are therefore less important than the first two joint construction.
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.