The principle is simple: turn the knob clockwise, the sharp thread turns all the way into the cork and pulls it out of the bottle neck. Turn the knob the other way and the sharp thread moves out of the cork and pushes it out of the corkscrew bell - for easy removal of the cork. The helical rings are intentionally designed to be very wide and flat: So they cut very gently into the cork. The bell corkscrew is equally suitable for natural and plastic corks.