Material
String, and what people do with it — measure, bind, count, tie off. Older than nearly everything else here.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Knot magic is one of the most widely recorded practices there is. Frazer gives a whole section to knots and rings as impediments: knots that were undone in a house where a woman was in labour, knots tied to bind a marriage or a wound, and the North Atlantic story of wind sold to sailors in a knotted cord, to be released one knot at a time. What runs through all of it is the same simple idea — a knot holds something, and untying it lets that something go.
A witch's ladder, a cord worked through with feathers, was found in a Somerset house and described in The Folk-Lore Journal in 1887. Nobody at the time could agree what it had been for, and the disagreement was published alongside the object, which is a good model for how this sort of evidence ought to be handled.
Modern use is continuous with all of it: red thread for protection, a cord knotted once per intention and untied to release, a length cut to a person's measure and kept. Do not tie thread tightly around a finger, a limb, or any animal — that is the only caution the material needs, and it is a real one.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
James Frazer, The Golden Bough (1890)
Frazer sets out the rule with unusual clarity: in a great many places nothing in a house was permitted to be knotted, locked or crossed while a birth was happening, because a knot anywhere was believed to hold things up everywhere. He notes that the same reasoning, run backwards, is what makes a deliberately tied knot a working.
Carried forward
Common in contemporary practice
Nine knots along a cord, one per part of an intention, tied while saying each aloud and untied in reverse when the thing is done or abandoned. Practitioners who use cord tend to keep it precisely because it can be undone.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.