Sailors are familiar with the sheet bend, a quick and easy method of joining two ropes that is secure enough for practical purposes. Bookbinders use the same knot, although few of them realize it.
The method shown below is especially useful in bookcrafts since the "old" thread length can be left quite short, as usually happens in practice. It plays little part in the knot formation. this method also has the advantage that the knot can be tied very close to the working part of the "old" thread.
The start of the knot is shown below. The needle is still attached to the "old" thread, and the needle lies through the noose of a simple slip knot tied in the "new" thread.
The slip knot is used to lassoo the "old" thread, and is gradually tightened and slid as far towards the last hole used by the "old" thread.
The slip knot is gradually tightened. When it is considered close enough to the paper the hold on the "old" thread can be released. The stage below can be taken at any time, but users will not wish the knot to have to be pulled through the next hole.
The next stage involves changing finger grips. Leave the "old" thread alone and pinch the loose end of the "new" thread with the fingers of one hand, and the working end of the "new" thread with the other. A quick pull will cause the noose to choke the "old" thread, pulling it right through the noose in such a way that it is unlikely ever to come undone. Snip the two ends to be 5 to 10 mm long and the job is done.
We have not shown pictures of the final stage in this, a working example. We have prepared a demonstration [XXXXXX]version in even more detail should you wish to clarify matters by seeing it in greater close up. Or better still - go and experiment. There is also guidance [xxxxxx] on typing a simple slip knot.
For anyone sceptical about the relationship with the sheet bend we have a few notes.
The method used by weavers to tie this knot is different. It involves wrapping threads around fingers. No doubt they are able to tie the knot in milliseconds, and with their eyes closed. Please let me know if you can amplify this. It may be a skill that is being lost to future generations.