These Retzuos started out as 15mm (as you can see the one on the left) and were stretched to the point where they are now less then 9mm (Retzuah on the right),
The preferable width is 11mm according to the Chazon Ish and 10mm according to Rav Chaim Naeh. The minimal width for making a Brachah is 9mm. If a Retzuah has been squeezed together at one spot making it less than the minimal width but it can be pulled back in to the minimal width it is acceptable . If however it has been stretched out and is narrower than the minimal width at any spot it must be replaced.
The end of the Retzuos may be cut on an angle even though they will be less than the minimal width.
Lesson: Do not tie the straps on very tight or wrap them on the box very tightly as this will lead to eventual stretching and invalidating the Tefillin straps
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There are Many things that can render Tefillin or Mezuzah not Kosher or at best minimally Kosher.
Some of which happen over time with aging and some unfortunately are Posul from the get go.
Letters, words and or Tagim that are missing, extra substituted, touching, Broken, Improperly Spaced, misshapen faded, cracked and weather damaged.
We document the problems we find and periodically upload them to the website.
We hope that this will educate and encourage the public to purchase only Tefillin and Mezuzas that are high quality from a reputable source, to take care of them properly and have them checked regularly.
Rabbi Kass was ordained by Rabbi Yisrael Meir Lau, former Ashkenazik Chief Rabbi of Israel. He is certified as a Sofer for both Kesivah and Hagoah by one of the leading experts in Safrus, Rabbi Avrohom Tzvi Vosner, Rav of the Vad Mishmeres Sta”m.