Is Sefardi ksav acceptable for an Ashkenazi?

Each letter of the alef-beis was transmitted from Hashem at Har Sinai in a general form. Deviating from this form invalidates the letter. Throughout the generations, different communities developed their own nuances in writing the letters. In the days of the Rishonim there were already distinctions between the ksav of the Ashkenazic and Sephardic communities. L’chatchilah, a person should only use tefillin which were written according to his tradition. B’dieved, one is yotzei if he uses tefillin written in any established ksav.

Except for hei and kuf, all the letters must be fully connected and cannot have any gaps or breaks in them. Sometimes a break will invalidate a letter, but it can be fixed (even out of sequence). In other cases--if the break is very large and the letter is no longer legible--fixing it once subsequent letters have been written is not a solution and the tefillin are pasul. Regarding a hei and kuf, the opposite is true: when their components are connected as one, the letters are pasul. Merely erasing the connection does not kasher the letter. The entire leg must be erased and rewritten. If the sofer already wrote subsequent letters, the tefillin are pasul.

What is the proper way to write a tag?

When writing Sta”m, the following letters need tagim: Shin, Ayin, Tes, Nun, “ende” Nun, Zayin, Gimel and Tzadi. Tagim are three “sticks” that come out of the top of the letter. On letters that have more than one roof, the tagim should come out of the left roof. Each tag looks like the letter zayin--a stick with a small square on its head. It is customary to make the middle tag slightly taller than the other ones. Care should be taken that the tag should not enter the air space of the letter above it.