A knot used to prevent the end of a string from slipping through a hole.
Stopper Knot
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References
Owen, P. Knots. Philadelphia, PA: Courage, p. 11, 1993.Referenced on Wolfram|Alpha
Stopper KnotCite this as:
Weisstein, Eric W. "Stopper Knot." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/StopperKnot.html