443. Sewing the Sheets of Parchment

Tefillin, Mezuzah v’Sefer Torah 9:12

Not fewer than three columns of text should be written on each sheet of parchment, nor more than eight. If a sheet of parchment is large enough for nine columns, it should be divided into two parts, one to hold five columns of text and the other to hold four. This is the rule at the beginning or the middle of a scroll. At the end of a scroll, even if there’s one verse in one column, that column may be written on a separate sheet of parchment and sewn to the others.

Tefillin, Mezuzah v’Sefer Torah 9:13

When sewing the sheets of parchment together, one uses only sinew from a kosher species of animal, even those that died without ritual slaughter or that were killed by predators. This is a law communicated to Moshe at Sinai. If one did not sew the sheets with sinew, or if he used sinew from a non-kosher animal, the sefer Torah is invalid until the threads are removed and resewn properly.