"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 ...
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known as a jackknife (jack-knife) or a penknife, though a penknife may also be a specific kind of pocketknife. A typical blade length is 5 to 15 centimetres (2 to 6 in). Pocketknives 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." - (en.wikipedia.org 15.09.2019)
