If the stitching of the Tefillin is severed, when are the Tefillin invalid?
Synopsis
The Mechaber follows the Rambam: two adjacent severed stitches or three severed stitches (even non-adjacent) invalidate old Tefillin but not new ones (as long as the titura holds). Other Rishonim are lenient about two stitches in all cases. The Rema cites the Rashi/Tur/Rosh view that it is the reverse (new invalid, old valid) and recommends stringency for both.
More in Tefillin on Chol HaMoed
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Discussion
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