What is the difference between the various ksovim used for STaM?

Halacha requires that Stam be written in the Ashuri script whose letter shapes follow the tradition of the Gemara and Rishonim, tracing back to Har Sinai. Ideally, this is to be transmitted in an unbroken chain or oral tradition. Yet, deviations from the accepted script don’t invalidate the letters b’dieved, provided they retain their correct basic forms.¹

The Rambam in Hilchos Tefillin doesn’t describe any specific script, presumably relying on the common knowledge in his time, and only cautions against misshaping letters, such as a beis that looks like a kaf.² The Sefardic Rishonim followed this general approach, without discussing and analyzing precise, nuanced guidelines for the script.³ But early on, a script conforming in many aspects to the mekubalim was adopted by the Sefardim, and became known as Ksav Vellish (or “Sefardi”).⁴

Conversely, the Ashkenazic Rishonim discussed and delved more into the nuances of the traditional script as transmitted by the sofrim of each generation.⁵ A thorough compilation, Baruch She’amar (15th century), is quoted in detail in the Beis Yosef, and this became known as Ksav Beis Yosef, in use by Ashkenazim.

The Arizal introduced variations to eight or nine letters in this Ksav Beis Yosef based on Kabbala. One major variation is that the left arm of several letters (e.g., tes) has a head like a zayin rather than a vav.⁶ This ksav, as described in the Kisvei HaArizal, became known as Ksav Arizal, in use by chassidim. Within each ksav, there were slight differing nuances, depending on the region and the styles of the sofrim.

All the ksavim are kosher, and represent varying traditions in the Ksav Ashuri dating back to the luchos given at Har Sinai. At the same time, one should endeavor to follow the mesora of their family and community. While some poskim raise an issue of tarti desasri with having mezuzos of varying ksavim on different doors of one home, in practice it’s permitted, though it’s hiddur that they should all be the same (see issue 265).

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