From the spools at the top, the threads pass through a thread guide, winding onto the spool fixed on a mobile rod at the center, and while the spindle turns, the doubled threads are distributed on the bobbin. If one of these threads breaks, the spool drops backward, and the shaft on which it is mounted, with its end in the form of an L, moves so that it gets stuck in the rods of the lantern cage mechanism, stopping the rotation of the spindle and preventing the device from wrapping with just one single thread on the bobbin.

This concept of a thread-break controlled stopping device, sometimes referred to as a catch thread device, is applied today in many spinning and weaving machines.