Using a folding knife is fairly simple once you understand how its mechanism works. For best handling, the blade must be held securely when open. That is why folding knives have locking or blade-retention systems. With so many systems available, a guide is useful for anyone unfamiliar with them.
Liner-based knives
Liner-based knives use steel or titanium metal liners as the basis for their locking mechanisms. These are true locks and among the safest systems. They include the liner lock, frame lock, and Axis lock.
Liner Lock
The liner lock is one of the most popular locking systems. It consists of two main metal liners, made of either steel or titanium, to which the handle scales are attached. One liner is shaped to act as a spring. When the knife is open, it presses against the base of the blade to prevent it from closing. Locking and unlocking are straightforward: use your thumb to push the spring liner sideways, then carefully fold the blade with your index finger. On some models, a button releases the locking liner. The liner lock is often confused with the thicker frame lock.
Frame Lock
The frame lock is easily confused with the liner lock because the mechanisms are similar. The difference is that a section of the handle frame itself presses against the base of the blade. This is why the system is also called an integral lock. To release the blade, push the spring section aside with your thumb. There are several frame-lock designs. On one version, the metal frame is covered by a handle scale; on another, it is exposed. A covered frame lock can be hard to distinguish from a liner lock. The frame lock can be considered an improvement, especially since its frame is often made of titanium.
Axis Lock
Introduced in 1998 on the Benchmade 710, the Axis Lock joined the range of folding-knife locking systems. It is associated with Benchmade knives, although other brands use similar mechanisms under different names. The Axis Lock is ambidextrous and allows one-handed operation with a flick of the wrist. The blade locks automatically when opened. To unlock it, simply pull the Axis button back. Although the liner lock is more widespread, the Axis Lock is presented here as the safer option.
Spring-lock knives
This category includes back locks and front locks. A spring operates the mechanism that locks and releases the blade.
Back lock
The back lock, or lockback, is a spring-operated locking system, as is the front lock with which it is often confused. The two work the same way; the only difference is whether the release is at the back or the front. The blade locks automatically when the knife opens, so you only need to act to unlock it. Pressing the release frees the locking bar so the knife can be closed. The French brand Florinox uses this mechanism, notably on its well-known Kiana model.
The locking collar
The locking collar is characteristic of traditional French folding knives. It is found on Nontron knives and, most notably, Opinel knives. That is why the mechanism is sometimes called the Opinel locking collar. The collar is a steel ring between the blade and the handle, with a fixed section and a rotating section. To lock the blade, simply turn the collar by hand; turn it back to unlock it.
The two-pin blade-retention system
Friction is the main principle behind this blade-retention system. It is often found on older knives because it is fairly simple. Friction between the blade and the handle scales helps hold the knife open. One pin forms the blade pivot, while another acts as a stop for the base of the blade. Piedmontese and Capucin knives fall into this category.
The Piedmontese mechanism
The Piedmontese mechanism is one of the oldest systems used on folding knives. Although knives with this mechanism are still called Vernantins, they are not necessarily Italian. Higonokami knives, small folding knives from Japan, also use this system. Piedmontese-style knives are easy to recognize: the base of the blade has a protrusion called a tab. Pressing it with your thumb opens the blade. When it rests against the back of the handle, it also holds the blade open.
The Capucin
The Capucin is recognizable by its handle, which is shaped like a monk’s hood. That shape gave the Capucin, or capuchin-style knife, its name. One of the oldest knives used by shepherds, it is simple and lightweight.
The slip-joint closure system
The slip-joint closure category includes standard slip joints, flat-spring joints, Slipits, and Notch joints. None of these systems has a true locking mechanism.
Slip joint
You are probably familiar with this closure system. The slip joint is found on most traditional regional French folding knives, such as the Laguiole and Sauveterre, as well as Swiss knives such as Victorinox models. It works through a spring along the top of the handle that presses against the base of the blade to help prevent accidental closing. However, light pressure on the back of the blade will close the knife easily. A slip joint is not a true lock: the blade can still fold at any time.
Flat-spring joint
The difference between a standard slip joint and a flat-spring joint is a notch at the end of the spring where it meets the base of the blade. This notch helps hold the blade more securely.
Spyderco systems
This section brings together the locking systems developed by the American brand Spyderco. There are two, both based primarily on compression: the ball bearing lock and the compression lock.
Ball Bearing Lock
As its name suggests, the ball bearing lock relies on a ball bearing. It was created by Spyderco, the well-known American brand with a spider logo. A piston pushes the ball into place. The ball is visible on both sides, making the system ambidextrous.
Compression lock
This is another folding-knife locking system developed and patented by Spyderco. Known for innovation, the American brand created a compression lock that is highly effective and easy to use. A liner near the top of the handle locks the blade in place. Releasing it with your thumb is simple.
Other folding-knife locking systems
This section covers systems developed by other manufacturers. It brings together a range of mechanisms without limiting them to a single common design.
Descy lock
This system resembles a variation on the ball bearing lock, but it has no ball. Instead, it uses a piston-inspired mechanism to lock the blade. Named after its maker, the Descy lock was developed by knifemaker Alain Descy.
Arc lock
Developed by SOG, this ambidextrous system can be operated with one hand. It is sturdy and keeps your fingers clear while locking the blade.
Action 2
Action 2 is a locking system found on automatic knives. A switch on the handle lets you change between automatic and manual operation. This system is specific to the Boker brand.
If you have read this far, you already know the main locking and blade-retention systems used on folding knives. We have listed the systems you are most likely to encounter. The list above is not exhaustive: folding-knife locks are numerous. It does, however, cover the main mechanisms; other models on the market are variations on them.