Editing Switchblade (section)

==== Single action OTF knives ====
[[File:Automatic knife out the front single action.svg|thumb|300px|Schematic of single action out the front automatic knife]]

A single action out the front knife operates under similar principles but will only automatically extend the blade which must then be manually retracted.

One spring post (green, left) is rigidly fixed to the handle (orange), the other spring post (green, right) is fastened to the base of the blade. The main spring (red) is under tension, but the blade cannot eject because the spring mounted button (light grey, its spring not shown) is resting in a notch in the blade. The cocking arm (blue) emerges through the base of the handle; friction with the handle holds it in place.

When the button is depressed (sideways into the handle or, as illustrated, into the page) a slot in it aligns with the blade and allows the blade to move forward. When the blade is fully extended flanges on the blade engage pins on the cocking arm retarding the blade's motion. The blade is locked in position when the rear notch of the blade allows the button to return to its rest position. Even if the button is pressed spring tension holds the knife open.

To retract the blade the button is again pressed so that its slot aligns with the blade. The cocking arm is pulled backwards which itself pulls the blade backward. When the blade is fully retracted the spring mounted button rests in the forward notch and again pops up and locks the blade in the cocked position. The cocking arm is then manually pushed forward to again sit flush with the handle.

Because the main spring is constantly acting on the blade and is extended by a far greater amount and is cocked by the whole hand and arm rather than by thumb the force it can exert on the blade is greater than with a double action knife. This will easily allow the tip of the blade to break skin when deployed and possibly penetrate a few millimetres (or hundredths of an inch) past it or to pass through light clothing. While still not a hugely strong design, because it is more firmly attached a good quality single action out the front blade displays less wobble and play than its comparable quality double action counterpart.