A pocket knife is a folding 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, cutting twine, performing an emergency tracheotomy, slicing a piece of fruit or even as a means of self-defense.
The earliest known pocket knives date to at least the early Iron Age. A pocket knife with bone handle was found at Hallstatt, dating to around 600-500 BC. Iberian folding-blade knives made by indigenous artisans and craftsmen and dating to the pre-Roman era have been found in Spain.
Peasant knife 
The peasant knife, farmer knife, or penny knife is the original and most basic design of folding pocket knife, 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.
Slip joint knife 
Most pocket knives for light duty are slip joints. 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 or affordable to most people 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 in size than most typical pocket knives.
Some popular styles of slipjoints are:
|Barlow||The Barlow knife has a characteristically long bolster, an elongated oval handle, and two blades. It is assumed to be named after its inventor, although there is some dispute as to which Barlow this actually was.|
|Camper||The traditional camper knife has a large drop point and shorter clip blade, along with a can opener, combination cap lifter/screwdriver, and an awl or punch|
|Canoe||The canoe knife has a handle shaped somewhat like a native American canoe and usually comes with two drop point blades|
|Congress||The congress knife has a convex front with a straight or shallow concave back. It usually carries four blades.|
|Elephant's toenail||The elephant's toenail is large design similar to the sunfish but usually tapers on one end giving it the "elephant's toenail" shape. These knives like the sunfish usually have two wide blades|
|Peanut||The peanut knife is a very small knife with one or two blades.|
|Penknife||The penknife was originally intended to sharpen quill pens, but continues to be used because of its suitability to fine or delicate work. A pen knife generally has one or two pen blades, and does not interfere with the appearance of dress clothes when carried in the pocket.|
|Sodbuster||The sodbuster has a simple handle with no bolster and usually only one blade.|
|Stockman||The stockman has a clip, a sheep's foot and a spey blade. They are usually middle-sized. There are straight handled and sowbelly versions.|
|Sunfish||The sunfish is a large design with a straight handle with two bolsters. The blades are usually short (less than 3 inches (76 mm)), but both the handle and blades are very wide. Sunfish knives usually have two blades.|
|Trapper||The trapper is larger knife with a clip and a spey blade. The blades are usually hinged at the same end.|
|Whittler||The whittler is a pattern of pen knife which has three blades, the master blade bearing on two springs.|
Multitool knives 
Multi-tool knives formerly consisted of variations on the American camper style or the Swiss Army knives manufactured by Victorinox, Wenger, and others. However, the concept of a multitool knife has undergone a revolution thanks in part to an avalanche of new styles, sizes, and tool presentation concepts. These new varieties often incorporate a pair of pliers and other tools in conjunction with one or more knife blade styles, either locking or non-locking.
Multitool knives often have more than one blade, including an assortment of knife blade edges (serrated, plain edged, saws) as well as a myriad of other tools such as bottle openers, corkscrews, and scissors. A large tool selection is the signature of the Swiss Army Knife. These knives are produced by Victorinox and Wenger and issued to the army and sold to the public. Similar to the Swiss Army knife is the German Army knife, with two blades opening from each side and featuring hard plastic grips and aluminum liners. The U.S. Military utility knife, issued by the United States Army, Navy, and Marine Corps, was made for many years by the Camillus Cutlery Company and Imperial Schrade. It was originally produced with carbon steel blades and brass liners (both vulnerable to corrosion), but with the arrival of Vietnam War was modified to incorporate all-stainless steel construction. The current-issue U.S. military utility knife has a textured stainless grips and four stainless blades/tools opening on both sides.
Miscellaneous designs 
Another style of folding, non-locking knife is the friction-folder. These use simple friction between the blade and scales to hold the blade in place once opened; an example is the Japanese higonokami.
An electrician's knife typically has a locking screwdriver blade but a non-locking knife blade. The two-blade Camillus Electirian's knife was the inspiration for the development of the linerlock.
A credit card knife is a very thin knife that is the shape and size of a credit card. It is designed to be carried in the wallet along with regular credit cards. Some credit card knives can contain other small tools, such as tweezers, or toothpicks.
Lock-blade knives 
Knives with locking blades, often referred to as lock-blade knives or clasp knives, have a locking mechanism that locks the blade into its fully opened position. This lock must be released in a distinct action before the knife can be folded. The lock-blade knife improves safety by preventing accidental blade closure while cutting. It is this locking blade feature that differentiates the lock-blade knife from either the peasant knife or the slipjoint spring-back knife.
Lock-blade knives have been dated to the 15th century. In Spain, one early lock-blade design was the Andalusian clasp knife popularly referred to as the navaja. Opinel knives use a twist lock, consisting of a metal ferrule or barrel ring that is rotated to lock the blade either open or closed. In the late 20th century lock-blade pocket knives were popularized and marketed on a wider scale. Companies such as Buck Knives, Camillus, Case, and Gerber, created a wide range of products with locks of various types. The most popular form, the lockback knife, was popularized by Buck Knives in the 1960s, so much that the eponymous term "buck knife" was used to refer to lockback knives that were not manufactured by Buck.
The lockback's blade locking mechanism is a refinement of the slipjoint design; both utilize a strong backspring located along the back of the knife. However, the lockback design incorporates a hook or lug on the backspring, which snaps into a corresponding notch on the blade's heel when the blade is fully opened, locking the blade into position. Closing the blade requires the user releasing the blade to apply pressure to the bar spring located towards the rear of the knife handle to disengage the hook from the notch and thus release the blade.
The Walker Linerlock and the framelock came to prominence in the 1980s. In both designs the liner inside the knife is spring-loaded to engage the rear of the blade when open and thus hold it in place. In the case of the framelock, the liner is the handle, itself. The Swiss Army knife product range has adopted dual linerlocks on their 111 mm models. Some models feature additional "positive" locks, which essentially ensure that the blade cannot close accidentally. CRKT has patented an "Auto-LAWKS" device, which features a second sliding switch on the hilt. It can operate as any liner-lock knife if so desired, but if the user slides the second control up after opening, it places a wedge between the liner-lock and the frame, preventing the lock from disengaging until the second device is disabled.
Tactical folding knife 
Buck's lockback knife was originally marketed as a "folding hunting knife" and while it became popular with sportsmen, it saw use with military personnel as it could perform a variety of tasks. Custom knife makers began making similar knives, in particular was knifemaker Bob Terzuola. Terzuola is credited with coining the phrase "Tactical Folder".
In the early 1990s, tactical folding knives became popular in the U.S.A. The trend began with custom knifemakers such as Bob Terzuola, Michael Walker, Allen Elishewitz, Mel Pardue, Ernest Emerson, Ken Onion, Chris Reeve, Rick Hinderer, Warren Thomas, and Warren Osbourne. These knives were most commonly built as linerlocks. Blade lengths varied from 3 to 12 inches (76 to 300 mm), but the most typical models never exceeded 4 inches (100 mm) in blade length for legal reasons in most US jurisdictions.
In response to the demand for these knives, production companies offered mass-produced tactical folding knives. Companies such as Benchmade, Kershaw Knives, Buck Knives, Gerber, CRKT and Spyderco collaborated with tactical knifemakers; in some cases retaining them as full-time designers. Tactical knifemakers such as Ernest Emerson and Chris Reeve went so far as to open their own mass-production factories.
There has been criticism against the notion of a "Tactical Folding Knife" when employed as a weapon instead of a utility tool. Students of knife-fighting point out that any locking mechanism can fail and that a folding knife regardless of lock strength can never be as reliable as a fixed-blade combat knife. Lynn Thompson, martial artist and CEO of Cold Steel pointed out in an article in Black Belt magazine that most tactical folding knives are too short to be of use in a knife fight and that even though he manufactures, sells, and carries a tactical folder, it is not ideal for fighting.
Other features 
Traditional folding knives are opened using nail-nicks, or slots where the user's fingernail would enter to pull the blade out of the handle. This became somewhat cumbersome and required use of two hands, so there were innovations to remedy that. The thumb-stud, a small stud on the blade that allows for one-handed opening, led the way for more innovations. One of these being the thumb hole: a Spyderco patent where the user presses the pad of his thumb against a hole and opens the blade by rotating his or her thumb similarly to using the thumb-stud. Another innovation of Sal Glesser, Spyderco founder, was the clip system, which he named a "Clip-it". Clips are usually metal or plastic and similar to the clips found on pens except thicker. Clips allow the knife to be easily accessible, while keeping it lint-free and unscathed by pocket items such as coins. Assisted opening systems have been pioneered by makers like Ken Onion with his "Speed-Safe" mechanism and Ernest Emerson's Wave system, where a hook catches the user's pocket upon removal and the blade is opened during a draw. One of the first one handed devices was the automatic spring release, also known as a switchblade. An innovation to pocket knives made possible by the thumb-stud is the replaceable blade insert developed in 1999 by Steven Overholt (U.S. Patent no. 6,574,868), originally marketed by TigerSharp Technologies and as of 2007 by Clauss. Some systems are somewhat between assisted opening and the normal thumb stud. CRKT knives designed by Kit Carson often incorporate a "Carson Flipper", which is a small protrusion on the back of the handle (when closed). By using an index finger and a very slight snapping of the wrist, the knife opens very quickly, appearing to operate like a spring assisted knife. When opened, the protrusion is between the base of the sharp blade and the users index finger, preventing any accidental slipping of the hand onto the blade. Some designs feature a second "Flipper" on the opposite side of the blade, forming a small "hilt guard" such as a fixed blade knife has, which can prevent another blade from sliding up into the hilt in combat.
Legal issues 
Pocket knives are legal to own in most countries, but may face legal restrictions on their use. While pocket knives are almost always designed as tools, they do have the potential to be considered by legal authorities as weapons.
In the United States, knife laws vary from state to state and even within different cities and counties of the same state. Some local jurisdictions prohibit the possession or use of pocket knives that feature locking blades. Others prohibit certain blade styles perceived by law enforcement and legal authorities as optimal for offensive fighting, transforming the pocket knife from a utility tool into a deadly weapon. These might include knives with dirk, dagger (double-edge), bowie, or stiletto blades. In some jurisdictions it is illegal to conceal knives larger than a certain size or with blades over a certain length, particularly when combined with locking blade mechanisms. The possession or carrying of a folding pocket knife with a quick-opening mechanism such as a gravity knife, butterfly knife, balisong, or switchblade may be prohibited. Under U.S. federal law, switchblades and ballistic knives are banned from interstate shipment, sale, or importation, or possession on federal or Indian lands or U.S. possessions and may be prohibited entirely in some states. Knives of any size or configuration may be prohibited by federal or state laws in certain designated areas or places, such as schools, courthouses, jails, power plants, or airports.
In the United Kingdom it is illegal to carry a knife having a blade more than 3 inches (76 mm) in length in public without "good reason". The terms "in public" and "good reason" are not defined, but examples of "religious duty", "national dress" and "requirement of employment or hobby" are given. It is left up to a police officer's individual subjective discretion, and ultimately a magistrate to decide if a knife is being carried "in public", and for a "good reason". Folding knives with blades of 3 inches (76 mm) or less may be carried without needing to provide "good reason" so long as the blade is not capable of being locked in the open position. However, it is illegal to have the intention of using any object in public as a weapon, meaning that even a knife that is legal to carry without needing "good reason" may still be found to be illegal if the police officer has grounds to suspect it will be used as a weapon. The onus lies on the officer to prove that intent. Recent court decisions in the U.K. have made it easier for public prosecutors to obtain knife possession convictions by preventing the accused from citing self-defence or even fear of attack as a justifiable reason for carrying a knife. The U.K. government advisory website on crime and justice states flatly that[not in citation given]"even if you carry a knife to protect yourself or make yourself feel safer but don’t intend to use it then you are committing a crime."
See also 
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- Lake, Ron; Centofante, Frank; Clay, Wayne (1995). How to Make Folding Knives: A Step-By-Step How-To. Krause. p. 190. ISBN 0-87341-390-3.
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- Levine, Bernard. 1993. Levine's Guide to Knives and their Values, 3rd edit. DBI Books. Northbrook, IL.
- Walker, Greg (1993). Battle Blades: A Professional's Guide to Combat/Fighting Knives. Boulder, Colorado: Paladin Press. pp. 37–38. ISBN 0-87364-732-7.
- Terzuola, Robert (2000). The Tactical Folding Knife: A Study of the Anatomy and Construction of the Liner-Locked Folder. Krause Publications. p. 47. ISBN 0-87341-858-1.
- Pacella, Gerard (2002). 100 Legendary Knives. Krause Publications. p. 101. ISBN 0-87349-417-2.
- Price, C. Houston; Mark D. Zalesky (2008). The Official Price Guide to Collector Knives, 15th edition. House of Collectibles. pp. 164–166. ISBN 978-0-375-72280-6.
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- Hopkins, Cameron (2000). "The Worse it Gets, the Better We Like It". American Handgunner Magazine 25 (157): 92–93
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- "British Knife Collectors Guild 'The Law' page". Retrieved 2006-11-19.
- Directgov.gov.uk, Crime and justice: Knife crime
- Media related to Pocket knives at Wikimedia Commons