A few more “bullets” to complete the siman:
▪ Although we learned that the ‘batim’ should preferably not be coated by anything other than paint, it would be kosher if a thicker layer was plated over it, provided that it was made of the hide of a kosher animal. This requirement precludes gold-plated tefillin, or the like!
▪ The stitching (Heb: ‘tefiros’) which is threaded through holes in the ‘titura’ (base of the ‘bayis’) must be made of kosher animal sinews (bigger animals are better, e.g. cows.) (Note: The animal need not be slaughtered according to halacha. The halacha is undecided as to whether or not the ‘Gid Hanasheh’ - sciatic sinew/nerve, which is forbidden by the Torah to eat - may be used for this purpose.) The sinews must be spun and twisted into fine thread, and this process must be done ‘lishmah’ (lit. for its sake, i.e. for the sake of the mitzvah of tefillin.) If sinews are not available, “strings” made of animal hide may be substituted until sinews become available.
▪ How are the sinews threaded through the ‘titura’?
Twelve holes are drilled from top to bottom through the ‘titura’. The sinews, threaded into needles, are sewn in a double layer, i.e. two needles are threaded through one hole; one needle threads to the left, while the other needle threads to the right. What emerges is that the threads completely cover the perimeter of the ‘titura’ - top and bottom.
▪ There is a custom, found in relatively few ‘batim shel rosh’ (but becoming more widespread), to pass additional threads through each of the three “spaces” that run between the compartments of the ‘bayis’.
▪ The ‘retzua’ (strap) of the ‘tefillin shel rosh’ is tied behind the head in the shape of the letter ‘dalet’. According to many opinions, this ‘dalet’ is the second letter of the word ‘Sha-d-ai’ – name of Hashem; the first being the ‘shin’ on the sides of the ‘bayis shel rosh’. There are several traditions about how the ‘dalet’ is formed and tied. According to the Mishnah Berura, the preferred is the ‘single dalet’; however, a ‘double dalet’ is also commonly used.
Question: We’ve got the ‘shin’ and the ‘dalet’; now Gimme a ‘yud’!
Answer: The ‘yud’ is represented in a knot as well - the knot which touches the inside corner of the ‘bayis shel yad’. In fact, one should take care that the ‘yud’ knot remains touching the ‘bayis’ at all times – even when it is put away! (Ed: That is why many pairs of tefillin have its yud-knot tied to the ‘bayis’ with a piece of sinew.