Serration is a

saw A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge. It is used to cut through material, very often wood, though sometimes metal or stone. The cut is made by placing the toothed edge against the material and mo ...

-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 When two objects touch, only a certain portion of their surface areas will be in contact with each other. This area of true contact, most often constitutes only a very small fraction of the apparent or ''nominal'' contact area. In relation to two c ...

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, tear ...

of some species, usually

sharks Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...

. 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, ste ...

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 distin ...

. Human uses of serration have copied, and gone beyond, those found in nature. For example, the teeth on a

or other

serrated blade A serrated blade is a type of blade used on saws and on some knives or scissors Scissors are hand-operated shearing tools. A pair of scissors consists of a pair of metal blades pivoted so that the sharpened edges slide against each oth ...

serves a similar cutting or scraping purpose as the serration of an animal tooth. Tailors use

pinking shears Pinking shears are scissors with saw-toothed instead of straight blades. They produce a zigzag pattern instead of a straight edge. Before pinking scissors were invented, a pinking punch or pinking iron was used to punch out a decorative hem on ...

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 a ...

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") and ...

s are made with serrated edges on the leather pieces, for no known purpose at all other than style. The

step clamp A step clamp is a type of serrated-edged clamp used in conjunction with step blocks in machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The pro ...

and step block assembly in metalworking adopt serration for the purpose of applying clamping pressure from an adjustable position.

References

External links

{{wiktionary, serrate, serrated, serration Cutting tools