Diagonal pliers (or wire cutters or diagonal cutting pliers) are pliers intended for the cutting of wire (they are generally not used to grab or turn anything). The plane defined by the cutting edges of the jaws intersects the joint rivet at an angle or "on a diagonal", hence the name. Instead of using a shearing action as with scissors, they cut by indenting and wedging the wire apart. The jaw edges are ground to a symmetrical "V" shape; thus the two jaws can be visualized to form the letter "X", as seen end-on when fully occluded. The pliers are made of tempered steel with inductive heating and quenching often used to selectively harden the jaws.
Diags or Dikes (a portmanteau of "Diagonal CutterS" is pronounced "dikes") – as in the phrase "a pair of dikes" or "hand me those dikes" – is jargon used especially in the electrical industry, to describe diagonal pliers. Dike can also be used as a verb, such as in the idiom "when in doubt, dike it out". This jargon has largely fallen out of use due to confusion with the semi-derogatory Dyke (slang).
In the United Kingdom and Ireland, diagonal pliers are commonly referred to as snips, and in Australia and Canada they are often referred to as side cutters.
The handles of diagonal cutting pliers are commonly insulated with a dip-type or shrink fit electrically-insulating material for comfort and some protection against electric shock.
Diagonal pliers are useful for cutting copper, brass, iron, aluminium and steel wire. Lower quality versions are generally not suitable for cutting tempered steel, such as piano wire, as the jaws are not hard enough. Attempting to cut such material will usually cause indentations to be made in the jaws, or a piece to break out of one or both jaws, thus ruining the tool. However higher quality side cutters can cut hardened steel, such as 2 mm piano wire.
For electronics work, special diagonal cutters that are ground flush to the apex of the cutting edge on one side of the jaws are often used. These flush-cutting pliers allow wires to be trimmed flush or nearly flush to a solder joint, avoiding the sharp tip left by symmetrical diagonal cutters. It is common for this type of diagonal cutter to be referred to by another name, such as "flush cutter" to distinguish it from symmetrical cutters.