Tefillin Gassot- Thick Phylacteries- are made, as the name suggests, using a particularly thick piece of leather. Tons of pressure are applied to the leather repeatedly using industrial presses in order to create the Tefillin. The Tefillin also feature inserts so as to ensure that the Tefillin close flat.
Due to the thick piece of leather used to make them, Tefillin Gassot are particularly durable and expected to last a lifetime. Even in the even of the Tefillin getting seriously damaged they can be repaired due to the quality of the leather used.
The straps of the Tefillin are made using the upper part of the hide- known in Hebrew as Retsu'ot Elyon- and the Batim of the Tefillin are 34-35 mm.
The Tefillin are made in Israel by Pe'er HaSTaM and come with a certificate proving their having been proofread by a computer and their Kashruth level. The Tefillin are also proofread by an expert.
Ktav Beit Yossef or Ari?
The most common script is called beit yosef since it is the form prescribed by Rabbi Yosef Caro in the Shulchan Aruch - the primary work of Jewish law. However, the great kabbalist Rabbi Yitzchak Luria Ashkenazi promoted a script that differs slightly from beit yosef script in nine letters of the alphabet. This script is called ktav ari - ari being the Hebrew acronym for Rabbi Yitzchak Luria. Most Ashkenazi, non-hassidic Jews, as well as most Sephardi Jews, use the beit yosef script, while most hassidic and kabalistically-oriented Jewish communities use the ktav ari script.
Ashkenazi Beit Yossef - generally used by those following Ashkenazi tradition, from Germany, England, Russia, Lithuanian
Ashkenazi Ari Zal - generally used by those following Chassidic Sefard tradition, from Poland, Galicia, Hungary, Romania, Slovakia
Outwards wrapping direction usually goes with Ktav Ari
Inwards wrapping direction usually goes with Ktav Beit Yossef.
Right or Left Handed:
If you are right-handed you wear the Tefillin on the left arm whereas if you are left-handed you wear the Tefillin on the right arm.