Stopper knots are primarily used to prevent the rope beeing pulled through a hole. Also these knots can be used to prevent small twine from fraying.
This is one of the most basic knots. Even a small child can do this intuitively. The knot itself is small, and hard to untie after heavy load. The untieing is greatly simplified leaving a drawloop (right drawing). This also makes the knot slightly bulkier and perhaps a little stronger. Do notice, that an overhand knot reduces the breaking strength of a rope by as much as 50%! So do not tie an overhand knot unnecessarily in the middle of a rope.
The figure-eight knot is an improvement of the basic overhand knot. It is a little bit bulkier, but much easier to untie. It is perhaps a bit stronger than the overhand knot. It may also be slipped, if wished. I recommend this knot to be used as a temporary stopper for rope and terminal knot for twine.
A beautiful stopper knot devised by Clifford W. Ashley. It is simple to tie, it is strong and bulky, and has a handsome threefoil symmetry when looked from the underside. To tie: Follow the first two drawings. This produces a knot much like the slipped overhand knot, only now the loop is from the standing part (the long part) of the rope, not from the short end. Tighten the overhand knot around the standing part first. Then pull the end of the rope through the loop as indicated in drawing 2. Finally, holding the body of the knot, pull on the standing part to nip the end under the loop (drawing 3). Use this knot, when the hole is too big for the figure-eight knot.