How Does a Dual Action OTF Knife Work?

An OTF knife is a knife whose blade extends and retracts from an opening at the front of the handle. When retracted, the blade is hidden within the handle. When the blade is extended “Out The Front,” it’s locked into place. It then cannot be pushed back in toward the handle except by either a retraction lever at the side of the handle or a slider switch near the front of one of the flat’s of the handle. Such a knife is considered to be dual action when the slider, which is pushed forward by the thumb to extend the blade, can be pulled backward by the thumb, retracting the blade. A single-action OTF knife is only able to automatically extend the blade. You have to pull the blade back into the handle by pulling a lever all the way to the back of the handle, which locks the blade in place until it is activated once again.

The mechanism inside a dual-action OTF knife is delicate and a patented device. These knives have a few basic internal structures in common which allow them to function properly. The mechanism is a flat plate the length of the knife’s handle sitting to one side of the blade. Holding the plate at either end is a coiled spring under tension, the force each exerts canceling out the other. The blade has an extended notch at the base. The slider on the handle is connected to a rocker switch which is connected to the metal plate. The small amount of force exerted by the user’s hand is what tips the balance between the two springs. When the slider is pressed forward, one of the springs is pushed slightly out of alignment. The other spring presses the metal plate forward, extending the blade and locking the notch into the base of the plate. When the slider is pulled back, the plate is popped free of the back of the blade, and the state of the two springs is reversed. The extended spring is compacted and misaligned, while the original misaligned spring extends to push against the top of the blade’s notch, retracting it.

It is a common belief that a dual-action OTF knife is capable of piercing through clothing and flesh when the blade is in the process of extending, such as when it is in your pocket or pressed up against someone’s body. This is a myth. People are mistaking an OTF knife with certain specialty knives that possess springs capable of exerting more than 40 or 50 lbs. in order to launch the blade out of the hilt and at an enemy. These knives are uniformly illegal and indeed capable of extending to pierce someone’s body from a retracted position. The springs of an OTF knife are barely capable of extending or retracting a blade on their own, and would be simply stopped from full extension if they contacted something as solid as human skin or thick cloth.