Sliding knife
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An out-the-front or "OTF" knife is also known as a "telescoping" or "sliding" knife. This is a type of mechanical system in which the blade of the knife is contained within the handle, and then slides parallel with the handle to deploy. Contrast this with the majority of knives, which are either "fixed blade" (having no mechanical operation) or are folding knives.
"Out-the-front" only describes the most basic portion of the knife's mechanical operation. OTF knives may be further subdivided into automatic knives, gravity knives, roll-locks, and other forms of operation.
OTF Gravity knives
An OTF gravity knife is a knife wherein the blade slides forward from inside the handle by force of gravity or inertia. The most famous OTF gravity knife is the Fallschirmjager-messer, or German paratrooper knife of World War Two.
OTF "Gentlemen's" knives
The simplicity of OTF mechanisms have allowed some knife manufacturers to build extremely thin gentlemen's models, that are very comfortable to pocket. Illustrated above are two very small OTF (telescoping) type knives, first a simple rocking jaw type button, and second a roll type button. With each, the leading edge of the jaw rests in a groove milled across the blade tang in order to lock.
OTF automatic knives (switchblades)
An out-the-front automatic knife's blade slides directly forward, out of the tip of the handle. There are two types of OTF (out the front) automatic knives: double action and single action.
Double action OTFs allow the user to extend or retract the blade with the press of a sliding button. Spring tension in these knives is actually provided by the movement of the button, which makes them much safer to carry since they will not open accidentally. However, the extra force the spring requires can also make intentional opening more difficult.
Single action OTFs require the user to retract the blade manually and compress the spring. Because they often use a lever to compress the spring, stronger springs can be used. This makes them open more vigorously than the double-action type, and allows them to achieve tighter lock-up.
Despite popular belief, OTF automatic knives are not utilized by pressing the undeployed knife against an opponent and then pushing the button, as the blade would most likely not deploy effectively when blocked. [citation needed] This is possibly a misbelief based on confusion with the ballistic knife.
Spring-assisted OTF gravity knives
Some civilian OTF gravity knives have a small helper spring to kick out the blade. This partial spring drive is not sufficient for collectors to classify this type of knife as a switchblade, because it does not drive the blade out to full lock.
Sheath-deployed telescoping knives
One knife type derived from the gravity knife is the telescoping knife which utilizes a specialized belt hanger/holsters that grasps the retracted blade so the it is pulled open when unholstering. Examples would include the Kershaw Ripcord. During the 1990s, a similar sheath-activated OTF knife was sold in the United States, claimed to be a police knife from the People's Republic of China. However, no proof of this assertion has been shown.