Automatic telescopic knife is a kind of tension spring energy storage. Its principle is to push the button forward and pull the tension spring, which is hooked on the blade through the pin. Because the blade is locked by a card at this time, the spring stretches to store energy.

　　Continue to push the button forward, the card is pressed by the button, and the blade is suddenly released. Under the elastic force of the spring, the handle is ejected, and another card is pressed by inertia, and it is locked again. Push the button backwards, and the opposite is true. The other is to rotate the knife, and the blade can only rotate and jump away, but can't retract.

　　This kind of knife is not self-retractable, and it needs to push and pull the protrusion on the side by hand. There is a spring and two sets of triggers in it. When the protrusion is slightly pushed and pulled, there will be no action. When it is pushed and pulled to a certain position, the lock of the cutter head will be unlocked, and the cutter head will be ejected or retracted under the elastic force of the spring and locked by another set of locking devices.