Serration is a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied pressure at each point of contact is greater and the points of contact are at a sharper angle to the material being cut. This causes a cutting action that involves many small splits in the surface of the material being cut, which cumulatively serve to cut the material along the line of the blade. In nature, serration is commonly seen in the cutting edge on the

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

of some species, usually sharks. However, it also appears on non-cutting surfaces, for example in botany where a toothed

leaf margin A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

or other plant part, such as the edge of a

carnation ''Dianthus caryophyllus'' (), commonly known as the carnation or clove pink, is a species of ''Dianthus''. It is likely native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years.Med ...

petal, is described as being serrated. A serrated leaf edge may reduce the force of wind and other natural elements. Probably the largest serrations on Earth occur on the skylines of mountains (the Spanish word ''sierra'', as in Sierra Nevada, means a saw). These occur both due to the uneven action of landform edges pushing rock upwards, and the uneven action of

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...

. Human uses of serration have copied, and gone beyond, those found in nature. For example, the teeth on a saw or other serrated blade serves a similar cutting or scraping purpose as the serration of an animal tooth. Tailors use pinking shears to cut cloth with a serrated edge, which, somewhat counterintuitively, reduces fraying by reducing the average length of a thread that may be pulled from the edge. A type of serration is also found in airframe shapes used in certain

stealth aircraft Stealth aircraft are designed to avoid detection using a variety of technologies that reduce reflection/emission of radar, infrared, visible light, radio frequency (RF) spectrum, and audio, collectively known as stealth technology. The F-117 N ...

, which use the jaggedness of the serrated edge to deflect radar signals from seams and edges where a straight, non-serrated edge would reflect radar signals back to the source.

Screw thread A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called ...

s show serration in profile, although they are usually shown in abbreviated or symbolic fashion on mechanical drawings to save time and ink.

Brogue shoe The brogue (derived from the Gaeilge ( Irish), and the Gaelic (Scottish) for "shoe") is a style of low-heeled shoe or boot traditionally characterised by multiple-piece, sturdy leather uppers with decorative perforations (or "broguing") an ...

s are made with serrated edges on the leather pieces, for no known purpose at all other than style. The step clamp and step block assembly in metalworking adopt serration for the purpose of applying clamping pressure from an adjustable position.

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{{wiktionary, serrate, serrated, serration Cutting tools