- Rav Ḥananel quotes Rav as teaching that the need for a base for the square tefillin, called the titora, is a halakha le-Moshe mi-Sinai.
- Abaye teaches that the hollow area through which the strap of the tefillin is pulled, called the ma’ebarta, is halakha le-Moshe mi-Sinai
- Similarly, Abaye teaches that the letter shin, formed in the leather or the tefillin shel rosh – tefillin worn on the head – is halakha le-Moshe mi-Sinai.
- Rabbi Yitzhak teaches that the rule requiring the leather straps of the tefillin to be black is a halakha le-Moshe mi-Sinai.
- A baraita is quoted as teaching that the requirement that tefillin must be square is a halakha le-Moshe mi-Sinai
The Gemara suggests relating this last requirement with the law that appears in a Mishna in Massekhet Megilla (24b), which warns that wearing round tefillin is dangerous and will not fulfill the mitzva. Rav Pappa argues that the Mishna in Massekhet Megilla may be talking about a different case – where the tefillin were made round like a nut with no base and there is concern lest the individual wearing such tefillin may crack his skull if he bangs his head while wearing them. The baraita is teaching that the squareness of the tefillin is a requirement.
Although the requirement that tefillin be made square is clearly presented by the Gemara as a halakha le-Moshe mi-Sinai, nevertheless, it appears from the discussion of the rishonim that this was only viewed as a necessity with regard to the tefillin shel rosh, but that the single parchment of the tefillin shel yad – tefillin worn on the arm – could be placed in a cylindrical leather covering if placed on a square base. Evidence of this practice can be found by examining the tefillin found in the Cairo geniza and in other illustrated manuals from the Medieval period.