The width of the straps must be equal to the length of a grain of barley. According to the Chazon Ish, the width must therefore be 11 millimeters, and according to HaRav Chaim Naeh, it must be 10 millimeters.
The knots of the Tefillin, both hand and head, are tied in accordance to the Halacha received by Moshe on Mt. Sinai. On the head Tefillin we make the knot in the form of the letter "Dalet" on the hand Tefillin we make the knot in the form of the letter "Yod”. These two letters, together with the letter "Shin" embossed on the head Tefillin, form the word "Shadai"
The "yod" knot must be attached to the "ketsitsa" (bayit).