9:15 A tallis may be made of two parts, which might be separated for laundering or sewing repairs and then rejoined. If the tallis is large enough so that a person could wrap himself in either of these two sections, then it is sufficient for the owner to remove two tzitzis strings from either side and reattach them when the garment is reassembled. If the tallis is not that large, he must remove and reattach all four tzitzis. This is because when the two parts of the garment are separated, each section loses its obligation in tzitzis. When the halves are reconnected, they are obligated in tzitzis again but, as we have said (in 9:6), one cannot tie tzitzis on an invalid garment and then fix the garment. If one of the two parts is large enough, the tzitzis only have to be removed from the part that is too small.
9:16 Let’s say that the corner is torn off of a tallis. If the severed piece is not three thumb-widths square, some authorities maintain that one may not reattach the piece and tie tzitzis onto it. This is because the broken corner is too small to be considered a garment in its own right so that even when it is reattached to the tallis it is still considered severed. The Kitzur Shulchan Aruch advises following the stringent opinion in this matter. If, however, the corner is not completely separated from the tallis, literally hanging on by a thread, then it is acceptable to reattach the corner and tie tzitzis on it. The practice is to sew on an extra piece of cloth at the corners of a tallis to ensure that it has a piece of cloth at least three thumb-widths square (as opposed to being made up of smaller pieces sewn together.)