A balisong, also known as a fan knife, butterfly knife or Batangas knife, is a type of folding pocketknife that originated in the Philippines. Its distinct features are two handles counter-rotating around the tang such that, when closed, the blade is concealed within grooves in the handles. A latch holds the handles together, typically mounted on the one facing the cutting edge (the "bite handle").
The balisong was commonly used by Filipinos, especially those in the Tagalog region, as a self-defense and pocket utility knife. Hollow-ground balisongs were also used as straight razors before conventional razors were available in the Philippines. In the hands of a trained user, the knife blade can be brought to bear quickly using one hand. Manipulations, called "flipping", are performed for art or amusement. Blunt "trainer" versions of these knives are available and can be used to practice tricks without the risk of injury.
The knife is now illegal or restricted in some countries, often under the same laws and for the same reasons that switchblades or concealed weapons are restricted. Within the Philippines, it is no longer as common in urban areas as in the past.
The name "balisong" is derived from barangay (village) Balisong, part of the municipality of Taal, Batangas province, which along with the neighboring barangay Pandayan, were the original manufacturing centers of the knives in the Philippines. The two barangays were home to a blacksmith industry that also produced other bladed implements such as bolo knives. It is also claimed that the meaning of the term balisong is derived from the Tagalog words baling sungay (literally, "broken/folding horn") as the hilt of the blade were traditionally made from carved carabao and deer horn, as well as bones. The traditional balisong is also known as veinte y nueve, or "twenty-nine," in the Philippines, because they are 29 cm (11 in) long when opened. Other names for the knives in English include "fan knives" and "butterfly knives" from the motion, and "click clacks" from the sound they make when they are opened and closed.
The origin of the knives is unclear. Oral histories claim that the knives were first created in the Philippines in 800 AD. However, there is no documentation or archeological evidence to back this. Balisong mass production in the Philippines can only be attested to the early 1900s. Another claim is that balisong were originally an adaptation of a French measuring tool called the pied du roi ("foot of the king"), invented between the 1500s to the late 1700s. However, how it was introduced to the Philippines is unknown. There are theories that it may have been introduced by sailors in the Spanish Empire, which was then allied to France.
Regardless of the origin, the modern balisong was perfected in the Philippines, where it became much larger and were predominantly used as a weapon and not just a tool. The quick opening techniques ("flipping") were also developed in the Philippines. In contrast, the French pied du roi was primarily a folding ruler, with the knife only included in some specimens as a novelty. They were cumbersome to open and unlikely to be used for self-defense, especially since they also commonly included a metal tang at a right angle from the end of the handle to aid in measuring. There were also very similar designs to the balisong produced in England in the late 19th century, presumably also derived from the pied du roi. But like the latter they were primarily utilitarian tools.
There are two main types of balisong construction: "sandwich construction" and "channel construction".
Sandwich constructed balisong knives are assembled in layers that are generally pinned or screwed together though may sometimes use a ball-bearing system. They allow the pivot pins to be adjusted more tightly without binding. When the knife is closed, the blade rests between the layers.
For a channel constructed balisong, the main part of each handle is formed from one piece of material. In this handle, a groove is created (either by folding, milling, or being integrally cast) in which the blade rests when the knife is closed. This style is regarded as being stronger than sandwich construction.
Some of the blades of traditional butterfly knives in the Philippines were made from steel taken from railroad tracks thus giving them a decent amount of durability and hardness, while others are made from the recycled leaf springs of vehicles.
Some balisongs, such as the Benchmade 51, do not use Tang Pins. Instead, it uses "Zen Pins", which are two small pins embedded in the handles of the balisong which make contact with the bottom of the blade. A balisong with zen pins negates the problem of having the tang pin fall out (as with some cheaper models).
- Bite handle
- The handle that closes on the sharp edge of the blade, and will cut the user if they are holding that handle when the knife closes. It's the handle that usually has the latch on it.
- The unsharpened portion of the blade just above the kicker, that makes it easier to sharpen the blade.
- Kicker (or Kick)
- Area on the blade that prevents the sharp edge from touching the inside of the handle and suffering damage. This is sometimes supplanted by an additional tang pin above the pivots.
- The standard locking system, which holds the knife closed. Magnets are occasionally used instead. Also keeps it from opening up when the user doesn't want it to.
- Latch, Batangas
- A latch that is attached to the bite handle.
- Latch, Manila
- A latch that is attached to the safe handle.
- Latch, Spring
- A latch that utilizes a spring to propel the latch open when the handles are squeezed.
- Latch gate
- A block inside the channel of the handles stopping the latch from impacting the blade.
- Pivot joint
- A pin about which the Tang/Blade/Handle assemblies pivot.
- Safe handle
- The handle (generally the handle without the latch) that closes on the non-sharpened edge of the blade.
- Unsharpened spine of the blade. Some balisongs are also sharpened here or on both sides with either a more traditional look or wavy edges similar to a Kris sword.
- The base of the blade where the handles are attached with pivot pins.
- Tang Pin(s)
- Pin meant to hold the blade away from the handle when closed to prevent dulling; and, in some cases, a second pin to keep the handles from excessively banging together while the butterfly knife is being manipulated.
- Zen Pins
- Screws mounted inside the handles that collide with the kicker mounted on the tang to prevent the blade from moving around while in the open or closed position.
- The blade is the piece of steel that runs down the center of the knife that is secured by both handles when closed. One edge of the blade is sharp and will cut the user if they are not careful, especially when flipping the knife. The other edge, called the swedge, is blunt and won't cut the user. The swedge commonly impacts the user's hand when flipping.
The balisong has been outlawed in several countries.
- In Australia, balisongs are generally classified as a prohibited weapon, which requires a special legitimate excuse to possess it. Australian Legal Definition: A flick knife (or other similar device) that has a blade which opens automatically by gravity or centripetal acceleration or by any pressure applied to a button, spring or device in or attached to the handle of the knife.
- In Belgium, butterfly knives are illegal.
- In Canada, although not specified by name as a prohibited weapon, the balisong knife is often considered by courts to fall under the "gravity knife" or a centripetal classification and is, therefore, prohibited, unless grandfathered in before prohibition.
- In the Czech republic, balisongs, switchblades and gravity knives are treated like normal knives.
- In Denmark, butterfly knives are illegal.
- In Finland, balisongs are legal to be purchased, sold and possessed, and are treated just like regular knives and befall under the edged weapons law. Carrying one in public is permitted if the person carrying one can prove it is used as a tool.
- In France, balisongs are legal to own if one is over 18 years of age but are illegal to carry without official authorization.
- In Germany, the balisong was outlawed when the Waffengesetz (weapons law) was tightened in April 2003 in the aftermath of the Erfurt massacre. Thus buying, possessing, lending, using, carrying, crafting, altering and trading it is illegal and is punishable by up to five years imprisonment, confiscation of the knife and a fine of up to €10,000. Using a butterfly knife for crime of any kind – as is any illegal weapon – is punishable by from 1 to 10 years imprisonment.
- In Hungary, balisongs, switchblades and gravity knives are treated like normal knives, they are legal to possess one regardless of its length, but it's illegal to carry one that's longer than 8 cm (3.14 inches) in public.
- In Ireland, butterfly knives are illegal offensive weapons.
- In Italy, balisongs are legal to own if not sharpened on both sides, but illegal to carry without justifiable reason.
- In Lithuania, balisongs among other knives are legal to possess and carry as they are not considered weapons. This excludes switchblades.
- In the Netherlands, balisongs are illegal.
- In New Zealand, balisongs are illegal.
- In Norway, balisongs are illegal.
- In the Philippines, it is now generally illegal to carry one without identification or a proper permit in the streets of the capital because of their prevalent use in crime and altercations. One now needs to demonstrate the need in professional livelihood or utilitarian purpose (such as cutting grass, preparing fruit and meat, being a vendor of knives, being martial arts instructors, etc.) to be able to walk around with bladed implements in the urban areas. Another rule of thumb is that the blade of pocket knives must not exceed the length of the palm and must not be openable by one hand in order to be considered as a utility knife as opposed to a weapon (thus, Swiss Army Knives are legal).
- In Poland, balisongs, switchblades and gravity knives are treated like normal knives.
- In Russia, balisongs are legal only if the length of the blade is not more than 90 mm.
- In Sweden, it's illegal to carry, import or trade a balisong; legal to own and collect.
- In Switzerland, balisongs are illegal to carry, give, lend, buy, or trade.
- In the United Kingdom, the balisong has been legally classified as an offensive weapon since January 1989. While they are legal to possess, carrying one in public is an offence under the Prevention of Crime Act 1953. Sale, lending, hiring, giving or importing is prohibited by the Criminal Justice Act 1988, as amended by the Offensive Weapons Act 1996. Any imported are liable to be seized and prosecution may follow. An exception is made for knives of this type over 100 years old, which are classed as antiques.
- In some parts of the United States, it is illegal to possess or carry such a knife in public. In certain jurisdictions, balisongs are categorized as a "gravity knife", "switchblade", or "dagger".
- In California, balisong/switchblade knives are legal to own, buy, sell, and transport if the length of the blade is not more than 2 inches. If the length of the blade is more than 2 inches they are illegal to buy, sell, transfer, or possess in public although it is legal to possess one if kept at home. (Penal Code section 17235 & 21510.)
- In Hawaii, it is illegal to possess, manufacture, sell, transfer, or transport any balisong/Butterfly-type knife.
- In Kansas, there were once legal restrictions on butterfly knives, however, as of July 2013[update], the Kansas Comprehensive Knife Rights Act decriminalized the carrying of all types of bladed weapons.
- In Illinois, it is legal to own and carry a butterfly knife.
- In Chicago it is illegal to carry concealed a knife with a blade longer than 2.5 inches. Concealed carry of a double-edged knife is prohibited. Automatic (switchblade) and gravity knives are prohibited.
- In Indiana it is legal to own and carry a butterfly knife both open or concealed.
- In Kentucky, the balisong is legal for concealed and open carrying anywhere one is not otherwise prohibited from carrying a concealed deadly weapon. Kentucky's constitution and revised statutes prohibit cities and counties from enacting weapons laws and restrictions.
- In Maine, it is legal to own sell and carry
- In Massachusetts, the balisong is legal for concealed and open carrying so long as it does not "[present] an objective threat of danger to a person of reasonable and average sensibility." Restrictions also apply depending on the area of the person carrying the knife (such as within a public school).
- In Michigan, the balisong is legal because it is classified as a "folding knife"
- In New Jersey the criminal law, NJSA 2C:39-1, suggests balisongs are illegal but the question of legality or illegality is an open question.
- In New Mexico, possession of a butterfly knife is illegal, because the butterfly knife is a "switchblade" within the meaning of the statute making possession of switchblades unlawful.
- In New York, the balisong has been determined not to be a gravity knife, and therefore not prohibited under the Penal Law [see: People v. Zuniga, 303 A.D.2d 773 (2nd Dept. 2003)] However, the law prohibiting gravity knives was found to be unconstitutional and their possession was decriminalized in 2019.
- In North Carolina, citizens are allowed to carry most pocketknives most of the time. Statute S.14-269, which prohibits the concealed carrying of any "bowie knife, dirk, dagger", or "other deadly weapon of like kind" doesn't apply to an "ordinary pocket knife carried in a closed position".
- In North Dakota, it is legal to own a balisong and carry it openly, however they are illegal to carry concealed, as they are considered to be deadly weapons.
- In Ohio, it is legal to own a balisong and carry it openly, and illegal to carry concealed, as it is considered a deadly weapon.
- in Oklahoma, the balisong is legal for open carry but is illegal to carry concealed.
- In Oregon, it is illegal to carry a concealed balisong.
- In Tennessee, there are no restrictions in carrying a balisong and similar knives, whether open or concealed carrying. Restrictions on these instead focuses on intent rather than merely carrying.
- In Texas, switchblades are legal as of 1 September 2013[update].
- In Utah, Balisongs are legal to own and carry as long as you are not a "Restricted Person" as described in Utah State Code §76-10-503.
- In Virginia, the balisong is legal for concealed, and open, carrying according to state law.
- In Washington, the balisong is classified as a "spring blade knife", and under state law one cannot manufacture, sell, dispose of, or possess such knives.
Balisong trainers feature a special blunt and unsharpened "blade" and are legal in some areas where balisongs are not.
- The Spy class in Team Fortress 2 uses a butterfly knife for his default melee weapon. It is also featured in the Spy's official machinima video, Meet the Spy, where the RED Spy uses his butterfly knife to take down the BLU Sniper.
- There is a set of weapon skins (cosmetic items) in the game Counter Strike: Global Offensive that swap out the default knife carried by the player model for a curved balisong. This was introduced in the 2014 Operation Breakout update. 
- A butterfly knife cosmetic set can be purchased for Octane in Apex Legends if the player obtains heirloom shards and purchases his set in the heirloom shop. This set was introduced during the System Override event in March 2020. 
- Fighting knife
- Filipino martial arts
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