Today again we wind cotton tread around the cones, as the musicians in former times always did. That has large advantages in relation to gluing cork:
1. The winding is easy to renew for everyone.
2. The many threads give much tension to the cone, so cracks cannot occur.
3. Shortening the instrument is no problem, if it sounds altogether too deeply.
If the threads become loose, that is mostly a note on the fact that the flute shrank. The mensur (interior drilling) has then changed and there can be adeterioration of the tuning and the sound. The instrument should be send back to the recorder-maker.
You should absolutely make certain that you don't turn the tap in the mortice (zapfenloch) back and forth. The two flute sections should be turned only in one direction of rotation, according to the direction of the thread-winding, quasi into one another like a screw. That way the thread will not become loose. In order to make the cones sufficently slidable You should use vaseline ore another gliding-paste.