Pin System

Pin Systems are used to keep the blade from hitting the inside of the the handles and to keep the handles from hitting each other. The latter is called slap.

Material Hardness

To understand the pros and cons of every pin system, it's important to first learn about material hardness.

Properly heat treated steel tends to be in the 58-60HR range, depending on the steel.
Unheat treated steel tends to be in the 35-41HR range.
Titanium tends to be around 36-38HR.

The higher the HRC number is, the harder the material is. The harder a material is, the more brittle it is, meaning it can snap, crack or shatter more easily. The exact opposite is the case for materials with a low HRC number, they become malleable. For example: The handles of the Canyon are very thin and are made out of heat-treated stainless steel and some users have reported that their handles have snapped after drops. While the Tsunami also has very thin handles, the handles are made out of titanium and the most titanium is going to do, is deform. That is because titanium has a much lower RC and is therefore less brittle.

While keeping in mind that higher RC materials are harder, and lower RC materials are softer and therefore more malleable, we can extrapolate that if two materials with different RC, the softer material will always give way to the harder material.

Different Pin Systems

There are currently 3 types of pin systems which balisongs utilize.
There are many different scales on which hardness can be measured, but the most widely-used for steel is the Rockwell Hardness scale C. It is often abbreviated to HRC.

Zen Pins

If the stopping mechanism is a stainless steel pin which sits in the handle, the mechanism is called a "Zen Pin"-system. There are multiple syles of zen pin systems, but they all have in common that a pin is inside the handle.

Press-fit

Press-fit Zen pins are typically only used in Channel balisongs, as this system depends on the structural rigidity that channel construction provides. A stainless steel pin is pressed into a hole which is slightly smaller than the pin itself, creating a tight Interference fit The pin is held in place by friction generated from the pin being slightly larger than the hole, ensuring it stays securely in place during use. An example of a balisong which uses this type of Pin system is the Krake Raken.

Screw Zen

The screw zen pin system uses a [threaded pin], or just a [threaded barrel]. This pin is usually held in place by a small cutout in the handle in which the pin snaps into place, making the screws redundant. While the barrel is usually held in place only by the screws. An example for a balisong with a screw zen pin system is the Replicant and an example for a screw barrel system, is the Telesto v3.

The screw zen system is sometimes called "Tunable zen system" which imples that they can be tuned. This is however wrong because if your balisong binds if you tighten the Zen screws, it does not mean that you tuned your screws wrong, it means that either there is something wrong your bushings, or washers.

Hidden Zen

Hidden Zens are only used in either Sandwich or Chanwich construction knives. That is because this style of construction requires a pin being placed inside the handles and this is only possible if there is a way to open up the handle, which is not possible on a Channel knive. An example for a sandwich construction knife with a hidden zen system is the Titanium Krake Raken and an example for a chanwich knife with a hidden zen system is the Tsunami.

Heat Treated vs Non Heat Treated Zen Pins

Heat treated zen pins run the risk of shattering, because the hard blade is hitting the hard zen pins, while non heat treated zen pins will deform over time, making the handle gap smaller, as described in #Material_Hardness. An example for a balisong which utilizes heat treated zen pins, is the Replicant. An example for a balisong which utilizes non heat treated zen pins, is the Krake Raken.

Tang Pins

Tang pins work very simmiliarly like press fit zen pins. The only difference is that a single pin is pressed inside the blade. An example for this type of pin system is the Alpha Beast 3.0.

Heat Treated vs Non Heat Treated Tang Pins

Tang pins must always be non heat treated, because this system relies on the tang giving way to the blade when it is pressed into the blade. If the tang is heat treated, the pressure of the hard tang can crack the blade. Another reason as to why the tang pin must always be non heat treated, is that the tang will make direct contact with the soft, titanium handles. In that case, both the soft tang pin and the soft titanium handles will have around the same HRC, so none of the two materials will give and none of the two materials will shatter due to a high hardness. So if the tang was heat treated, it would be much harder than the handles and the handles would give way to the tang pin and that would cause slapping.

Pinsless

The pinsless system tries to achieve the same clean aesthetic as hidden zen pins, but with a channel construction. Instead of using a zen pin, the area of the handle where the pin would normally be inserted is left unmachined. This uncut section of the handle itself acts as a built-in pin, eliminating the need for a pin. An example of a knife with a pinsless design is the JK Monarch

This type of pin system (or lack thereof) has received significant criticism, as it is considered the most prone to failure. Over time, it can lead to the development of slap, due to the repeated stress on the unmachined section of the handle acting as a stop pin.