The Retzuot are drawn through the base of the Tefillin cases, and bind the cases (Batim) to the arm and head while wearing Tefillin.
The Retzuot are made from the hide of a kosher animal. It is preferable to use the hide of a Behama Gasa(cow or ox) but some make the Retzuot from sheep or goat (Behama Daka) hide, even if this is of lesser quality.
The straps (Retzuot) must be black. The source of this rule is Halacha L’Moshe M’Sinai. It is important to take care that the black ink on the straps not peel or become rubbed away.

Our rabbis determined a set width for the Retzuot.  They must be the width of a grain of wheat or barley: 0.9 cm according to the more lenient view, 1.1 cm according to the stricter opinion. If they are narrower, the Retzuot should be replaced.

Halacha does not determine a set length for the Retzuot. The optimal length is:
Tefillin shel Yad: Long enough to wind around the hand.
Tefillin shel Rosh: Long enough to hand down in front of the body.

At Tefillin Hebron, we prepare the Retzuot from the hide of a Behama Gasa, since it is strong and long-lasting. The Retzuot are made to the proper length according to Halacha and painted with quality black coloring that lasts.
Knots in the Form of the Letters Dalet and Yod in the Retzuot

By means of tying special knots in the Retzuot, it is customary to form the letters Dalet ד  and Yod י . This completes, along with the letter Shin incised in the Tefillin shel Rosh, the word Sha-dai, one of the names of the Almighty.
We tie a knot in the Retzuah of the Tefillin shel Rosh in the shape of the letter Dalet.
We tie a knot in the Retzuah of the Tefillin shel Yad in the shape of the letter Yod, and draw it near to the Ma’abarta.

At Tefillin Hebron, we are especially careful to tie the knots properly to form the letters Dalet and Yod according to Halacha. Adding these to the Shin in the Tefillin shel Rosh, we are happy to have the privilege of bringing HaShem’s Name into our Tefillin!