Halakha Ulangan 22:12: Mishneh Torah, Fringes & Mishneh Torah, Tefillin, Mezuzah and the Torah Scroll

The fringe that is attached to the corner of the garment, and made of the same species of material as the garment, is called Tzitzith Fringes, because it is like the fringes of hair of the head, as it is said, "And he took me up by the lock (Tzitzith) of my head" (Ezekiel 8:3). This fringe is called "the White (part)", because we are not commanded to dye it. No definite number of threads is prescribed in the Torah for the fringes.

How are the fringes attached? One begins at the corner of the garment, that is, at the edge of the woven cloth, and measures off a length not greater than three finger-breadths and not less than the length between the base of the thumbnail and the first joint. Four threads are inserted there and turned down in the middle, so that eight twined threads are pendent from the corner, The eight threads are not to be less than four finger-breadths long. If longer, even as much as one or two cubits, they are fit for use. The breadth of the thumb is the standard for all finger-breadths. One of the eight threads should be blue, and seven should be white.

So too if one inserts fringes in a garment with three corners and then makes a fourth corner and inserts a fringe in it, the fringes are all unfit for use, for it is said, "Thou shalt make fringes" (Deuteronomy 22:12) and not use those already made.