Clasp-knife

A pocketknife is a foldable knife with one or more blades that fit inside the handle that can still fit in a pocket. It is also known as a jackknife or jack-knife. A typical blade length is 5 to 15 centimetres (2 to 6 in). Pocket knives are versatile tools, and may be used for anything from opening an envelope, to cutting twine, slicing a piece of fruit or even as a means of self-defense.

The earliest known pocketknives date to at least the early Iron Age. A pocketknife with a bone handle was found at the Hallstatt Culture type site in Austria, dating to around 600-500 BCE.Iberian folding-blade knives made by indigenous artisans and craftsmen and dating to the pre-Roman era have been found in Spain.

The peasant knife, farmer knife, or penny knife is the original and most basic design of a folding pocketknife, using a simple pivoted blade that folds in and out of the handle freely, without a backspring, slipjoint, or blade locking mechanism. The first peasant knives date to the pre-Roman era, but were not widely distributed nor affordable by most people until the advent of limited production of such knives in cutlery centers such as Sheffield, England commencing around 1650, with large-scale production starting around the year 1700 with models such as Fuller's Penny Knife and the Wharncliffe Knife. Some peasant knives used a bolster or tensioning screw at the blade to apply friction to the blade tang in order to keep the blade in the open position. The smallest (Nos. 2 -5) Opinel knives are an example of the peasant knife. The knife's low cost made it a favorite of small farmers, herdsmen, and gardeners in Europe and the Americas during the late 19th and early 20th century.

Most pocket knives for light duty are slipjoints. This means that the blade does not lock but, once opened, is held in place by tension from a flat bar or leaf-type backspring that allows the blade to fold if a certain amount of pressure is applied. The first spring-back knives were developed around 1660 in England, but were not widely available until the arrival of the Industrial Revolution and the development of machinery capable of mass production. Most locking knives have only one blade that is as large as can be fitted into the handle, because the locking mechanism relies on the spring along the back of the blade to lock it and it is difficult to build in multiple levers, one for each blade. Slipjoints tend to be smaller than other typical pocket knives.

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Wikipedia