The batim (boxes)
Tefillin consist of a set of two Batim (Boxes): The one worn on the arm, called “Bayit Shel Yad”, and the other worn on the head, called “Bayit Shel Rosh”.
Shel Yad
The Bayit Shel Yad is smooth on the outside and contains an inner hollow cavity.
Shel Rosh
The Bayit Shel Rosh has 3 grooves along its length and 4 inner hollow spaces.
In order to be kosher, the Batim must be:
Colored black
Perfectly square on top
Perfectly square on the bottom
Contain square stitches
Contain grooves from the top to the seam (in the Bayit Shel Rosh)
Types of Batim:
There are two main types of Batim:
1. Those made from cowhide (“Gassot”)
2. Those made from sheepskin (“Dakkot”)
How the tefillin are wrapped < > Cowhide (gassot)