This is actually the easiest method of binding.
The sewn book block is very thin with hotmelt glued and haven't got a cover.
As for the spine is not required to fix a cover, we can glue with a very thin layer and provides
this combination (thin layer of glue, and nothing against glued) to a maximum lay-flat
with a minimum of glue-intrusion.
Often chosen to start and finish with 4 pages on 250 grams board for the firmness.
Colored sewing thread is a common option in this technique.Spine width 5-55 mm.