שדי — a Name assembled out of three pieces of leather

Shin on the head-box. Dalet in the knot behind the head. Yod in the knot at the arm-box. Together: שדי — Shaddai, and this app already reads that Name elsewhere as she-amar dai, "the One who said ENOUGH" — the divine brake, and the Name of Yesod.

⭐ What deserves attention is not that a Name appears. It is how. The Name is not written on the tefillin. There is no ink involved and no surface bearing it. One letter is raised out of a box, and the other two are knots — shapes made by tying something. So the Name exists only across three physically separate objects, on two different parts of a body, held in place by tension, and it is assembled by the act of putting them on. Take the tefillin off and lay them on a table and the Name is still there, technically, in pieces. It is a Name that is completed by being worn.

⚠ Layer, carefully: the shin is old and required. The knots are old and required too, and Menachot 35b treats the form of the knot as received tradition. But reading the two knots as a dalet and a yod, and the three together as Shaddai, is a later identification — medieval, and thoroughly standard by the time it reaches the codes. It is worth knowing which part is the specification and which part is the reading, even when the reading is beautiful and even when everyone has agreed on it for eight hundred years.