Home Tefillin Check

Source:
The Tractate Manachot 45a, teaches that the square-ness of Tefillin is a law that was given verbally to Moshe on Mount Sinai. Explains Rav Pappa, this square-ness is referring to the stiching and the angles.
The Law:
The square-ness applies to 3 areas: Biet Ti'tora square-ness of the stiching
1) Biet
The length and width of the Tefillin must be equal and the diagonal 1 and 2/5 larger then the width or length. Example:
When to go and ask your Rabbi?
If there is a one percent difference between sizes of the width of the Tefillin. Example: 1% difference table: (for usual size Tefillin) Width Length 29mm 28.71mm 30mm 29.70mm 31mm 30.69mm 32mm 31.68mm 33mm 32.67mm 34mm 33.66mm 35mm 34.65mm 36mm 35.64mm 37mm 36.63mm
When the lack of square-ness is recognizable to the eye. Example:
Note:According to my experience with the Craftsman here at Tefillin Beit E-l, a deviation of 1/3 mm is easily noted with the expert eye. (You should ask your Rabbi)
Says Zichron Eliyahu, 7:9:6 p.98, "the measurement is according to an expert eye".
Walls of Tefillin need to be straight. Example:
When Tefillin become damaged. If damaged 1mm or more the Tefillin are not kosher however may be fixed. If the damage is less then 1 mm however there is a round appearence to the Tefillin it is not kosher and should be fixed. In summary: Go ask your Rabbi. Example:
Good news:
Good news. If damaged, even larger then 1mm, but is entirely on the roof of the Tefillin, the Tefillin are can be blessed upon. Note:A hole will pasul the Tefillin any where on the Katzizah, biet, cube of the Tefillin.
Tefillin Compartments. If damaged 1mm or more the Tefillin are not kosher however may be fixed. In summary: Go ask your Rabbi. Example:
Protruding Compartments. If one biet, compartment of the head Tefillin protrudes more then a 1mm the Tefillin are not kosher however may be fixed. In summary: Go ask your Rabbi. Example:
Square in Square. If recognizable that the beit is not square in the frame of the tutorah, base of the Tefillin you must ask your Rabbi. Example:
Conclusion:
Firstly: Thank you to the Sefer Zichron Eliyahu where most of the above information was taken. Secondly: I hope the above information will help all the Jews fulfill the mitzva of Tefillin in its completeness.