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.

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.

Properly heat-treated steel typically falls in the 58-60HRC range, depending on the steel.
Non-heat-treated steel is generally around 35-41HRC.
Titanium usually has a hardness of about 36-38HRC.

The higher the HRC number, the harder the material. Harder materials are more brittle, which means they are more prone to snapping, cracking or shattering. Softer materials (lower HRC) are more malleable and deform under stress rather than breaking. For example: The handles of the Canyon are very thin and are made out of heat-treated stainless steel. Some users have reported that their handles have snapped after drops. Meanwhile, the Slift V2 also has very thin handles, but they are made of titanium. Rather than snapping, titanium will generally just deform because of its lower hardness.

If two materials that both have a high HRC hit against each other, one, if not both of those materials will be at risk of snapping, cracking or shattering.
If two materials with different hardness ratings make contact, the softer one will always yield to the harder one, meaning that the softer material will get squised and deformed. If two materials that both have a low HRC hit against each other, both of those materials with squish and deform each other, but the ammount is very small.

Different Pin Systems

There are currently three types of pin systems used in balisongs.

Zen Pins

If the stopping mechanism is a stainless steel pin housed inside the handle, it is called a "zen pin" system. There are multiple implementations of zen pin systems, but they all have in common that a pin is inside the handle.

Zen pins can be found on both aluminium and titanium balisongs.

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.

Glued

Glued zen pins are usually only found on cheap balisongs. They function the same way as #Press-fit zen pins, with the only difference being that they are held in place with adhesive, rather than by friction. As a result, they tend to fall out much more easily. If a glued zen pin comes loose, it can usually be reinstalled using Loctite or another suitable adhesive.

Screw Zen

The screw zen system is only used in Construction#Channel or Construction#Sandwich construction knives. The screw zen pin system uses a [threaded shoulder pin], or just a [threaded barrel]. Threaded shoulder pins are usually held in place by a small cutout in the handle in which the pin snaps into place, making the screws not necessarry for this type of construction to work. The barrels, however, are usually held in place by just the screws. An example for a balisong with a threaded shoulder pin is the Replicant and an example of a screw barrel system is the Telesto v3.

The screw zen system is sometimes called "Tunable zen system", implying that it can be tuned. This is however misleading because if your balisong binds when tightening the zen screws, the issue usually never lies with the screws, but with the bushings, or washers. If you want to learn more about this, check out Pivot_System#Unexpected_Binding.

Hidden Zen

Hidden zen pins are only used in Construction#Sandwich or Construction#Chanwich construction knives. This is because placing the pin inside the handle requires the handle to be be disassembled, which is not possible on a Construction#Channel knive. An example for a Construction#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.

Shielded Zen

Shielded Zen pins function the exact same way as #Hidden_Zen pins, except that they are used on a channel knives. A small section which includes the section around the pivot screws is removed from the handle and a slot for the zen pin is machined into the handle, simmiliar to a #Press-fit setup. Once the zen pin is installed, the removed section is reattatched and held in place by the pivot screw. This pin system was invented by Jimpy. Here is a video demonstration: https://www.instagram.com/p/CzzWaUkPGBy/

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 gradually 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 similarily to press fit zen pins. The biggest 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.

While there are tang pin balisongs with aluminum handles, such as the Nautilus, tang pins generally do not work well with aluminium. This is because the unhardened tang pin is still significantly harder than aluminium, causing the aluminium handles to deform over time. As a result, the handle gap will degrade, eventually leading to slap

Heat Treated vs Non Heat Treated Tang Pins

Tang pins must always be non heat treated, this is because the pin needs to conform to the shape of the hole in the blade during the press-fit process. If the tang was hardened, pressing it into the blade could cause the blade to crack due to the lack of give in both the blade, and the tang pin. Additionally, tang pins directly contact the soft titanium handles. By not heat-treating the tang pin, both materials should have similar hardness, allowing them to deform slightly and absorb impact without causing damange. If the pin were heat-treated, it would be significantly harder than the titanium, causing the titanium to deform and eventually leading to slap.

Pinsless

The pinsless system attempts 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 part of the handle acts acts as a built-in pin. An example of a knife with a pinsless design is the JK Monarch

Due to the difference in hardness between the hardened blade and the soft titanium handles, this type of pin system (or lack thereof) will inevitably cause the handle gap to degrade over time, eventaully leading to slap.