451. Techeiles

Tzitzis 1:2

We take a string of wool dyed the color of the sky and wind it around this fringe. This string is called techeiles (blue). The Torah did not set a fixed number of times that this string must be wound.

Tzitzis 1:3

The mitzvah of tzitzis contains two commandments: to make a fringe on the corner of the garment and to wind the techeiles around the fringe, as per Numbers 15:38, “You shall make fringes... you shall place on the fringes of the corner a string of techeiles.”