A butterfly knife, also known as a fan knife and in the Philipines as the balisong, is a folding pocket knife. Its distinction is two handles counter-rotating around the tang such that, when closed, the blade is concealed within grooves in the handles. It is sometimes called a Batangas knife, after the Tagalog province of Batangas in the Philippines, where it is traditionally made.
The balisong was commonly used by Filipino people, especially those in the Tagalog region, as a self-defense and pocket utility knife. A common stereotype is that a Batangueno carries one everywhere he or she goes
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 versions of these knives, called “trainers”, are for sale to practice tricks without the risk of injury.
The knife is now illegal or restricted in many countries, often under the same laws and for the same reasons that switchblades are restricted, and in their country of origin they are no longer as common in urban areas as they were.
While the meaning of the term balisong is not entirely clear, a popular belief is that it is derived from the Tagalog words baling sungay (literally, “broken/folding horn”) as they were originally made from carved carabao and stag horn.Balisong is also the name of a barangay in the town of Taal, Batangas province, which became famous for crafting these knives.The traditional balisong is said to be called the veinte y nueve because they are 29 centimeters long when opened, while another story goes that it is named after a lone Batangueno who fought off 29 assailants using one. These knives are also referred to as “fan knives” and “butterfly knives” from the motion and “click clacks” from the sound they make when they are opened and closed.
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, like 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.
- Bite handle
- The handle that closes on the sharp edge of the blade, and will cut the user if they are holding the handle when they go to close it. 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 whilst 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 of the sides of the knife is sharp and has a high chance of cutting the user, the other side has no potential chance of cutting the user, but it is still important for the user to be careful.