Nicks that Can Upset the Rebua (Square) of the Tefillin
Inadequately Blackened Tefillin
Pasting the Compartments of the Shel Rosh Together
Nicks that can upset the rebua (square) of the tefillin
The tefillin must be square at every level, from the bottom of the titura until the top of the bayis. If the tefillin become nicked and lose the rebua at any level, they are pasul. The Mishna Berura is uncertain as to what size nick would disqualify tefillin. Even according to the stringent approach, a very tiny nick is not a problem.If the corners round out a bit, they remain kosher if they still look square. It is possible to rely on the chazaka and not inspect the rebua on a daily basis.
The bayis, titura and ma’avarta (channel in the back of the tefillin where the retzua passes) must all be black. The poskim debate whether this rule is a halacha l’Moshe m’Sinai or a mitzval’chatchila m’drabonon, and it should be treated stringently as a doraisa. Any shade of black is kosher, but ideally these areas should be as black as a raven. The paint should not have a thick consistency that will flake off easily and it and certainly should not peel easily.
Pasting the compartments of the shel rosh together
Ideally, the four compartments of the shel rosh should not be completely connected to one another but should be connected enough to prevent them from separating. The tefillin are kosher if the bayis was made from one hide and the compartments are separated at least on the outer side with clearly delineated lines. If the bayis is made from multiple hides, its kosher status is the subject of a machlokes.
A halacha l’Moshe m’Sinai mandates that the tefillin be square. This includes the titura, the stitching that holds the titura closed, and the entire height. A beracha is not recited if the bayis is not square.
The poskim note that as long as it seems square to the eye, it is kosher and it is unnecessary to use calibers or other modern measuring tools to perfect the square.
The bayis (both the shel yad and shel rosh) must be fashioned from one piece of hide. The poskim debate whether two hides sewn together or attached with glue can be reckoned as one.
The forms of the shins on the side of the shel rosh