397. Sewing the Boxes Shut

Tefillin, Mezuzah v’Sefer Torah 3:9

The tefillin must only be sewn shut using sinew from a kosher species of domestic or wild animal, including animals that died without ritual slaughtered or that were torn by predators. The practice is to use sinew from the heel of the animal, which are white. If the sinews are too firm, they are softened with stones until they become like flax. They are then spun and twisted into thread and used to sew tefillin and the pages of Torah scrolls.

Tefillin, Mezuzah v’Sefer Torah 3:10

When tefillin are sewn shut, they must be sewn in a square. The common practice is to make three stitches on each side so that there will be twelve stitches in total. This applies to both the tefillin of the arm and the tefillin of the head. However, if one made ten stitches or fourteen stitches, it is of no consequence. The thread for each stitch must pass through on both sides.