1. Do the compartments ("batim") of the tefillin of the head need to be "perudos" – completely separated from one another, down to the base?
"The separation between the "batim" must reach to the stitch (at the base of the tefillin" (Shulchan Aruch, Orach Chaim 32:40). The Vilna Gaon and the Chasam Sofer were stringent about this and ruled that if this condition is not met, the tefillin are posul -- not usable for the mitzvah.
Nevertheless, the Mishnah Berurah writes that in order that the "batim" not get ruined, it is better to that the separations reach just a bit more than half way down to the stitch, and in the bottom half of the box, inside of it, the "batim" are glued together. Even if the "batim" are glued together more than that, still, so long as a slight slit remains at the very top of the box, so that the "batim" are separated a bit, the tefillin are kosher (Biur Halacha on 32:40, citing the Chai Adam).
2. Must the boxes of the head tefillin and the arm tefillin be equal in size?
No, this is not in any way considered "hidur" (beautification of the) mitzvah.
3. If the boxes of the tefillin are nicely painted, is this considered "hidur" mitzvah?
"It is a mitzvah to enhance their appearance – on their outsides as well as regarding their insides and what they contain there (Ramah 32:4).
The implication is that the verse, "Zeh kaili v'onveihu – This is my G-d and I shall glorify Him" includes even things which are concealed from view. Accordingly, one should not make any sign of identification on tefillin, even if the sign is concealed.
4. What is the halacha if, on the box of the tefillin of the head, the painter made counterfeit slit between the batim, not where the actual separation exists?
The tefillin are posul – unusable for the mitzvah. However, if on the top of the box, as well as on the top half of its sides, there is no discrepancy between his slits and the real ones, the tefillin are kosher (Mishnah Berurah, 32:40).
5. In the old days, the leather on the underside of the tefillin (the "lower titura") was a separate piece of leather that was sewn on to the remainder (i.e. to the "upper titura" that holds the parchments). Today, the upper and lower "titura" are all one piece of leather that is folded over and stitched together so that the tefillin are closed and the parchments in the upper titura are protected. After the stitching, is one allowed to add glue so that the lower titura remains firmly attached?
Technically i.e. according to the straight letter of the law, it is permitted (Biur Halacha on 32:51), but some are stringent not to do so (Chazon Ish 11:10).
6. Must both tefillin boxes be perfectly square? If not, how much less than perfect is permitted?
One needs to take care that the imperfection is not noticeable to the naked eye. If the discrepancy reaches one millimeter, the tefillin are unfit for the mitzvah. For the sake of "hidur" (beautification of the mitzvah) one should to make sure that the discrepancy is no more than one per cent, which usually translates to between 0.3 and 0.4 of a millimeter.
7. What care must taken about the "matlit" i.e. the piece of parchment (or animal skin) that serves (inside the tefillin boxes) as a protective covering over the parshiot of the tefillin?
Preferably, there should be no markings or letters written on it. Also, its width should be sufficient to cover the entire width of the parchment on which the parshiot are written (Mishnat HaSofer 22:3).
One should not switch a "matlit" from one parsha and use it to cover a different parsha (Imrei Sheffer 18:2).
It need not be made of skin (or parchment) that was worked for the sake of the mitzvah of tefillin. It can even be made of cloth (Mishnah Berurah 32:106-7).
8. One hears of a "hidur" called "mikuvanot." What is it?
The thread that is used to make tefillin is called "gid," for it is made of "gid" i.e. sinew (of a kosher animal). "Mikuvanot" is a way of stitching the head tefillin so that it is obvious that "gid" passes between the four compartments of the box. For this purpose six tiny holes are drilled in the base of the tefillin – three on each side of the box, exactly opposite from where each separating slit between the "batim" reaches the base of the tefillin. Afterwards, the "gid" is threaded between the "batim" and through these holes so that the "gid" that goes between the "batim" is seen clearly.
This is a desired beautification of the mitzvah, because many Rishonim maintain that "gid" must pass between the "batim" in order to make it obvious that the batim are separate compartments. This "hidur" – where the "gid" is clearly apparent on upper side of the tefillin base, directly across from the required actual separations, makes it patently clear that the separations exist.
There is an additional benefit of having the separation of the "batim" accentuated by means of this "hidur." Placement of the tiny holes where the actual separations meet the top of the base makes it impossible for a painter of the tefillin to make a "counterfeit" slit in a place other than where the actual separation is found.
9. In terms of length and width, the tefillin must be perfectly square. In accomplishing this, is it important that the final "shaving" not be done with a device that is powered by electricity? Is it important that the device's blade do the shaving by means of man-power i.e. a foot pedal?
One need not be particular about this, for even if the shaving device is powered by electricity, man-power is present, too (Minchas Shlomo, Chelek 2, 4:9).
10. The "ma'avarta" is the part of the tefillin which serves as a passageway for the tefillin strap to pass through the tefillin's base so that the tefillin can be affixed to the head or arm. When making tefillin, some attach a thin piece of animal skin to the whole underside of the upper "titura," by cutting a square hole in it so that the parchments still can be placed into the box. The added piece of skin forms an elevating ridge that assures that when the top and bottom of the tefillin are sewn together, there is sufficient room in the "ma'avarta" for the strap to pass through it. Is it more beautification of the mitzvah if the tefillin are made without this additional piece of skin?
No, the major authorities have ruled that that there is no source for the contention that doing without the added piece beautifies the mitzvah (Zichron Eliyahu 70:22).
11. If the twelve holes that are made in the "titura" for the sake of sewing the tefillin together are larger than they should be, do the tefillin remain kosher?
Just as the tefillin box, when viewed from above, must be perfectly square (as perfect as possible), and so, too, the upper and lower "titura" of the tefillin, the appearance of the tefillin's stitching around the box must be the same. Therefore, atop the upper "titura," if the holes through which the "gid" is passed are too large in diameter, danger exists that the appearance of the stitching no longer will be square, particularly if the oversized holes are at the corners. Still, if to the eye, the stitching creates lines that form a square, the tefillin remain kosher, even if due to the size of the holes, the "gid" that enters each hole on one side does not touch the "gid" that exits that hole on the other side (Shevet HaLevi, Chelek 5, Siman 14). It is preferable to be quite careful about this matter (Ohr L'Zion 1:4).
12. If the "titura" of the tefillin has cracks, crevices, holes or other such imperfections, is one permitted to fill them in with powdered leather?
Some say that the entire "titura" must be of one piece of leather. Preferably, therefore, the square shape of the upper or lower "titura" should not be restored this way (Shevet HaLevi, Chelek 3, Siman 2). Some authorities are lenient (Minchas Yitzchak, Chelek 6:1). (One needs to pay particular attention to the part of the "titura" next to the "ma'avarta," because in that place, quite often, cracks or folds appear that spoil the square shape of the "titura."
13. How big must the tefillin be?
The "titura" (not including the "ma'avarta" should be no smaller that two finger-widths by two finger-widths (Mishnah Berurah 32:41). According to R. Chaim Noy, this translates to four square centimeters while according the Chazon Ish it translates to five square centimeters.
Some say that for the sake of "hidur" mitzvah, the box itself should not be smaller than this. (Such tefillin, which are larger than the normal, are called "Shimushi Rabbah").
For both the head and arm tefillin, there is no minimum measure for the height of the box, but some say that for the sake of "hidur" mitzvah, the box's height should be no different from its length and width (Divrei Yatziv 1:22, interpreting the words of the Rambam and Arizal).
14. Regarding the parchments upon which the parshiot are written, must all of each parchment be tucked into the hollow of the box, so it is isolated in its own compartment, or can some of the parchment protrude beyond where the box ends, into the area across from upper "titura" and even into the hollow of the "titura"?
Preferably, each parchment should be completely inside the hollow of the box, inside its own compartment, and not reach below the place across from where the box meets the base of the upper "titura." According to the straight letter of the law, however, the parchments can protrude beyond that point into the area opposite the entire width of the upper "titura" (Some are stringent, as is written in the Shlah).
Although one or more of the parchments might protrude to the point where they are opposite the "feeter" (an added piece of skin glued onto the upper "titura" at the lip of the compartments) the tefillin remain kosher (See above, that this piece of skin is added to assure that there will be enough space in the "ma'avarta" for the tefillin strap to pass through). Despite the protrusion of the parchment to this point, the tefillin remain kosher even according to the opinion that glue does not cause any addition to become "one" with the rest of the tefillin, for the added piece of skin is considered "nullified," as if it is simply an extension of the box itself (Zichron Eliyahu p.23).
According to the Sephardic custom, one should avoid letting any parchment protrude beyond the hollow of the box itself. The Responsa Yabiah Omer says that protrusion beyond that point makes the tefillin "posul" (unusable for the mitzvah).
15. Can one cut the parchments so they are small enough to fit into the batim?
Most poskim (legal authorities) permit it, even if the parshiot were already used in different tefillin (Mahrshag 1:310:5 and Machtzis HaShekel 32:10). Some are stringent not to ever cut the parchments (Minchas Yitzchak, Chelek 6:5).
16. If glue is used in the making of the tefillin, if it is glue made from an animal, must the animal be kosher?
Yes, but synthetic glue is equally acceptable (Mishnah Berurah 32:220; Chazon Ish, Tefillin 11:9). Some are stringent, though, not to use synthetic glue.
17. Regarding the letter shin that appears on the outside of the tefillin of the head, must it be in the same style of writing as that of the parchments?
It does not have to be, but it is preferable for the sake of beautifying the mitzvah (Mikdosh M'aht 34:75).
18. If "gid" tears during stitching, is one allowed to tie onto it another piece of "gid"?
No, the piece that tore must be removed and one must start again. On the other hand, before starting to stitch, if one sees that the piece of "gid" is too short, one is allowed to tie on a second piece to it (Magen Avraham 32:68).
19. What is the halacha where the paint on a tefillin box is thick and one sees that it is possible to peel it off, but underneath that place the box is still sufficiently black?
"It is good if the paint is an indistinguishable part of the box. Paint that is thick and can be peeled off into individual pieces make the tefillin unfit for use" (Mishnah Berurah 32:185). Thick paint that can be peeled off is considered a tangible object in its own right, resting upon the tefillin, intervening between the tefillin and the air, as if the tefillin have a cover atop them.
20. Before being placed inside the box, the parchments of the tefillin are enwrapped in an "outer" strip of parchment ("matlit" – see above) and a piece of "gid" is tied on to keep the wrapping in place. Regarding the tefillin of the head, the "gid" used to tie in place the wrapping around the parsha "V'hiya im shamoa-h" is supposed to emit from the inner compartment and be visible on the outside of the tefillin. What if this requirement is not fulfilled and this piece of "gid" does not appear?
It does not hinder the mitzvah. Still (for a Kabbalistic reason), it is preferable to attend to the matter so that that particular piece of "gid" is visible outside of the tefillin, in the required place next to the box (Shevet HaLevi, Chelek 4:1).