Tefillin phylacteries, are leather boxes filled with Torah verses on the Unity of God, the Exodus, and mitzvot. They are worn during morning prayers, except on Shabbat and Holidays. Tefillin boxes fare crafted from molded leather; their straps are also leather; Upon its parchments are the handwritten verses. All elements are held to a very precise specifications, so one should only purchase tefillin(a single lifetime purchase) from a trusted source—like Judaism.com, who only sells pre-checked Tefillin and Mezuzahs from its most reliable sources in New York and Israel.
Shopping Tips: Tefillin
Before purchasing tefillin it is important to know the following:
1. Are you left handed or right handed. The hand/arm tefillin goes on the opposite - the "weaker arm."
2. To which "nusach" (custom) do you subscribe: Ashkenaz (wraps the arm straps away from the body): Sfard and Chabad (wraps the arm straps toward the body). This affects how the knot is tied to the arm tefillin.