There are two types of safrus lettering: Ashkenaz and S’faradi. Ashkenaz breaks down into Beis Yosef K’sav and Ari Zal K’sav. Most people of Lithuanian descent use Beis Yosef K’sav. Most people of Eastern European descent (including all Chasidim) use Ari Zal K’sav. The Labovitch Chasidim use Ari Zal K’sav or Alter Rebbe K’sav which is a type of Ari Zal K’sav.
There are several differences between the Beis Yosef and the Ari Zal in how to make some of the letters. The most significant difference is the letter ‘tzadik’. In K’sav Beis Yosef a tzadik is made by joining a yud to a nun. In K’sav Ari Zal a tzadik is made by joining a backwards yud to a nun. The question is: How do we know that a backwards yud attached to a nun is kosher?
In the past fifteen years I have read many sources that indicate that a person who does not follow the Ari Zal’s customs in general should not use Ari Zal K’sav. Practically speaking, I have rarely heard of a rov who poskens that a person should replace his mezuzos or tefillin if they are Ari Zal K’sav and his minhag is Beis Yosef or vice versa.
One of my customers is a true Yekee (he follows the customs of the German Jewish community). Since he has tefillin that are written in Ari Zal K’sav, I thought I would let him know. He in turn asked Reb Feival Zimmerman, the Rav of Gateshead, also a Yekee. He poskened that my customer need not worry about it, and there is no reason for him to change his parshios.
Another customer told me that he received his tefillin from his father who received them from his father. After many years he had his tefillin checked and found that the shel rosh was k’sav ari and the shel yad was k’sav beis yosef. He asked Reb Dovid Feinstein what the halacha is in such a case and Reb Dovid Feinstein told him that this is a case of tartei d’sasrei (two things which contridict each other) and that they need to be replaced.
Of course, you should not rely on the story for p’sak halacha. If you should find yourself in this situtation you should consult with a rabbi.
