Sewing a sefer Torah
1. The sheets of a sefer Torah are sewn together, and it is halakha from Moses at Sinai that they be sewn only with the sinews of a ritually pure animal or beast. If the sinews were from a ritually impure species, the sewing is invalid until it is removed and done properly. One should not buy sinew from non-Jews because they may be from ritually impure species. It is not clear whether one may use the gid ha-nase, since this may not be eaten (Benei Yonah); it seems to me that stringency is proper.
2. We use the sinews from the heels of cattle and wild animals, because they are white. If they are hard, we beat them with stones until they resemble flax. Then they are spun and twisted, and used to sew tefillin and the sheets of sifrei Torah (Rambam). Ox sinews are best for sewing.
3. When sewing the sheets, one shouldn’t sew from the very top to the very bottom, but should leave an unsewn space at each end so that the sheet will not tear in the middle when it is rolled. All the rest is stitched, the sewing being on the outside. Post facto it is valid if the ends were not left unsewn (Ran).
4. It is the custom to glue patches over the seam at the top and bottom to strengthen it, but some question this. In any case, one should take care not to glue the patches at the very edge; there should be a space at the top and bottom with no sewing and no patch. One need not use kosher glue for these patches, as they only strengthen, they aren’t essential, but ideally one uses kosher glue all the same (Benei Yonah citing Imrei Noam).
5. A roller is attached to each end of the sefer Torah, the long margins which were left at each end being wrapped around the rollers and stitched in place with sinew. The roller should be longer than the page by two etzbaot at each end. It is forbidden to glue the sheets around the rollers, because eventually the glue will dry up and the rollers will fall off (Benei Yonah citing Imrei Noam).
6. If a small part of a seam between sheets was torn, one may read from the sefer exactly as normal [even if there are other sefarim available], but if more than half of the seam was torn, it may not be read from, even if it had already been taken out [of the aron]; it must be returned and another sefer brought out. If they have no other sefer, and the tear is in the same book that they are going to read from, they may only read from it if at least five stitches remain. However, if the tear is in another book, they may read from it even if there are only two stitches left.
7. If any sheet hadn’t been sewn in, the sefer may not be read from, even if the sheet was placed with the sefer.