Sutra:
113. ettizhaiyAy mUnRu saradAyiruppathoru mangaLaSUthram pOlE thirumanthram.

Meaning:
This thirumanthram, made up of eight strands (the eight aksharas) and three threads (the three parts), is like the holy thread used in a marriage.

Sri PBA Swami's Sarartha Deepikai:
In this world (in some cultures) we see that a woman wears a holy thread in marriage which signifies that she is wedded to someone and cannot belong to anyone else. Similarly, the faith in the Thirumantram shows that the chEtana belongs to the Lord and no one else. Therefore, the Thirumantram is like the holy thread used in a marriage.

Unlike the worldly holy thread which is made up of sixteen strands and two threads, the Thirumantram is made up of eight strands and three threads. The eight divine aksharas are the eight strands and the three parts are the three threads.