Page 128 - Patrick Moreau-Marine "Knots How to Tie 40 Essential Knots"

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This is a knot that sailors have been using since the dawn of time.
Using the button strap knot, you can grab any rope, moor objects, a sheet,
etc. Just before tying the bosun’s whistle knot to make a button, tie a simple half
knot in the middle of the rope.