Measurements relating to a sefer Torah – the blank spaces
1. The lower margin measures four etzbaot [thumbs, see above, 13:1] and the upper margin three (because the upper margin does not get as much handling as the lower). The space between columns measures two, and accordingly one must leave an extra etzba at the beginning and end of each sheet to allow for sewing, so that when it is sewn the distance between columns will be two etzbaot uniformly throughout the sefer. Between each line there should be a space one line high, and between each of the Five Books there should be four empty lines, the next book starting at the beginning of the fifth line. At the beginning and end of the sefer there should be enough klaf to wrap around the roller, plus an additional two etzbaot to go between the last column and the roller.
2. The four lines which are left between the Five Books are a very good thing to do, but they are not critical to the validity – he may decrease or increase the number. However, if he leaves no space at all, the sefer is invalid, and accordingly, if he didn’t even leave enough space to make it a petuḥa paragraph, the sefer Torah is invalid even post facto.
3. Some opinions say that one should take care not to finish one book at the end of one column and start the next book at the top of the subsequent column, even if he does leave four lines between them, but should have the end of one book, the four lines between, and the beginning of the next book all on the same column (R’ Yitzḥak b. Avraham in Tosafot, Bava Batra 13b, citing the Yerushalmi). It is correct to try to do this where possible, but if one absolutely cannot, he may finish one book at the end of one column and start the next book at the beginning of the next column, provided he leaves four lines between them. It doesn’t matter whether the four lines are all at the end of the column, all at the beginning of the column, or divided between them (Tosafot and Tashba”tz, ibid.).
4. One should not make his writing smaller on account of the space at top and bottom. That is to say, if he had scored all the lines and had not left three etzbaot above the top line, but could not remove the lines, and accordingly wanted to squash the top line so as to make the top margin the right size – he shouldn’t, because it will make the writing look speckly [ie conspicuously uneven]. Rather, since it’s too late to fix it, he shouldn’t worry about the size of the margin (Taz). The same applies for the spacing between the lines – that is, if he ruled two lines in the middle of the sheet which were too close together, he shouldn’t reduce the size of his writing so as to leave the prescribed width between the lines (Talmud, Rashi).
5. Neither should he reduce the size of his writing on account of the spacing between paragraphs. For instance, consider a parsha setuma, which has a space in the middle [of the line] and writing on both sides. One should not squash up his writing so as to fit it at the end of the line, but should make sure from the start of the line that he will have enough space without having to squash his letters. If it does happen, the custom is to make small letters – that is, the height is the same as the other letters, but they are narrower. He shouldn’t narrow his quill, but should keep the same nib width he used for the other letters, since then he is not altering the writing too much.
6. If one had a five-letter word at the end of the line, he should not write two letters within the column and three without, but three within and two without. If there isn’t space to write three letters, he should leave the place blank. One may even write two letters of a three-letter word in the margin, since at least some of it is inside the column. However, one may not write a two-letter word in the margin, even if the two letters are part of a longer word and just happen to spell a word of themselves. Some permit this (Sha”kh) (see above, 10:15, for how this affects the letters of the Name).
7. If one had to write a word of ten letters, more or less, and didn’t have space to write the whole word within the line, according to the Rambam he should write it if he can get half in the column and half outside, and according to the Rosh he still shouldn’t write more than two letters outside the line, and it is proper to be stringent (Sha”kh).
8. The contents of the last two chapters, unless otherwise specified, are the best way to do it, but it is still valid if one does it differently, even if he wrote a whole word outside the line (the space between the word and the line being like the ordinary spacing between words), or even if he wrote two such, provided he does not fill the whole space between columns, as then the reader will not know whether the extra words belong at the beginning of one line or at the end of the line in the previous column. Post facto, anything is valid provided it is clear where it belongs (Benei Yonah).