Min haTorah, the method of making tzitzis is as follows: The strings are tied to the garment with a double knot. Then the longest string is wrapped around the other seven strings three times and they are tied together with a double knot. Mid’rabonon, additional knots and krichos (wrappings) are necessary. In total, there should be five sets of double knots. The number five corresponds to the Chamisha Chumshei Torah. These knots also serve to protect to the original knot, which is required min haTorah. The ten single knots correspond to the Eser Sefiros.
[שו"ע יא, יד, ומשנ"ב סה; וראה ביה"ל י, ד"ה ונתקו; וראה ביאורים ומוספים דרשו, 76]