One overhand knot, is a very simple thing - although not as simple as many people think, if they have not yet realized the many distinct geometrical forms it can have ( and as we know, it is the geometry that matters most in practical knots, not the topology ).
One overhand knot tied around ONE tensioned line, is not a simple thing any more !

The penetrating line may go through any one of the three different "openings" of a tightly closed overhand knot, the angle between its axis and the axis of the line the overhand knot is tied on may vary, and it can be pulled towards the one or the other direction. So, if we are going to use one overhand knot to nip and immobilize such a tensioned penetrating line, we have to think a little bit

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One overhand knot tied around TWO tensioned lines, becomes a complex thing, because it can take many different, geometrically, forms - therefore there are many ways - some more and some less efficient than the others - to use an overhand knot as the nub of a two-wrap tight hitch. I will try some housekeeping, continuing this thread, where I had first realized how effective an overhand-knot-based nub of a tight two-wrap hitch can become.
Those hitches belong to one of two general classes, depending on the orientation of the overhand knots. In the first the overhand knots are laying on the surface of the pole "belly up" (bu), and in the second "belly down" (bd).
Let me show some pictures of hitches belonging to the second class, and I will tell more about them in another post.
For the moment, the one very important thing that I would like to mention, right from the beginning, is that the hitches which can be pre-tensioned by pulling their ends against the pole ( = perpendicularly to the surface of the hitched object ), without this resulting to any major deformation of their nubs ( which deformation may result in their loosening ), are the most useful, because they can become the most tight. This was the reason I had abandoned the simple-hitch-a-la-Gleipnir, and all those Gleipnir-like hitches ( some of them shown in the attached pictures ) where the nipping loop of the Gleipnir has been replaced by an overhand knot : the orientation of their ends as they enter/exit their nubs is not what we would had wished. The same happens with hitches where the overhand knot has been used to enhance the gripping power of a Clove hitch, a Strangle, or a Constrictor ( see the third attached picture ). When we pull the one end against the pole, the whole nub is set in motion, it loses its stable position on the surface of the pole ( or even, as it happens in some cases, it is severely deformed ), and we lose some of the tight grip which we have managed to gather by the pulling of the other end. All those hitches are meant to be pre-tensioned tightly by pulling the one end after the other, so we do not wish the next pulling, of the second end, to interfere to what we had already achieved by the previous pulling of the first end.