Why does the Torah enjoin us regarding techelet? Because techelet resembles sapphire, and the Tablets were made of sapphire, to tell you that as long as Bnei Yisrael gaze upon this techelet they are reminded of what is inscribed on the Tablets and observe the commandments, therefore it is written, ‘And you shall see it [the techelet string] and remember all of the commandments of G-d and you shall do them.’ - Mishnat Rabbi Eliezer, Chap. 14
|Type of Strings||Used to tie|
|Rambam||Rambam with 13 chulyot, Chabad/Arizal, "Sephardic"
|Raavad 7||Amram Gaon 7|
|Raavad short||Gra, Chinuch, Raavad, Amram Gaon 13, Rav Schachter 3x7
|Tosafot||Tosafot, any of the above|