In reply to Denislejeune:
By way of a spot of history - larger nuts always used to be tied on a length of rope - 6-9mm usually, depending on size. 5mm was not confidence inspiring until dyneema/spectra/whatever came along. To cut to the chase, I'm not aware of one of those breaking at the knot (double fisherman's) - if they did break, it was where they went through the nut. Getting them undone involved a teaspoon as a marline spike, or a knife, but if you had the whole length you could more easily measure the new length against it. When undone, the rope inside the knot was always bright and shiny, as opposed to the faded and worn stuff outside the knot. I wouldn't worry, and if you take a load strong enough to break a piece of rope there, your spine will probably join it for solidarity.