I have wondered for some time about certain elements of Chabad minhagim re. tefillin, so here goes:
What is the origin of their kesher shel yad?(asked elsewhere)
- When was it decided that they should be huge (4x4cm or larger)
- Why must they be mikshah (made of one piece)?
- Why is their ש different from both the Arizal ש and the written form of the Alter Rebbe ש? What is the source for this?
I'm sure there are other concerns which I have missed, but these are the main factors which make them unique, in my opinion.