What is the Minimum Width of Tefillin Straps?

What is the minimum width of tefillin straps?

For example: if one's tefillin straps partially tore, how much is required to remain for the tefillin to remain Kosher?

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Shulchan Aruch Orach Chaim 27:11 says that the straps should be at least the width of a grain of barley. The Halacha Berura says that this amounts to 1 cm, or 2/5th of an inch, but one should preferably ensure that the Tefillin be at least 1.1 cm, or .44 inches, wide.

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This. From Sefer Hamitzvot too - How are the straps made? We take leather straps [at least] the length of a barley-corn in width. If they are wider than that, they are acceptable. – zaq Aug 2 '11 at 19:52

Rambam rules (Tefillin 3:12) that the minimum width for the straps is a barleycorn. In :19 he notes that anything narrower is invalid.

The Semag (Aseh #22) rules that the straps should be between a barleycorn and the width of a grain of wheat (I'm not sure how big that is). If they are wider or narrower than that, though, they remain valid.

Rosh and the Tur (OC 27) rule that a barleycorn is the ideal width, but they too accept that narrower straps are kosher.

The Shulchan Aruch (OC 27:11) rules that straps narrower than a barleycorn should still be worn (it seems with a Bracha) when no other straps are available. While the Mishna Berura there limits this to where the straps are at least the width of a grain of wheat, the Aruch haShulchan there (27:22) does not and calls the whole requirement for any minimum width only a Hiddur Mitzva.

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Interesting, because wheat grains are smaller than barley. I would also point out that those who use the מה שעיניו רואות approach to shiurim would find equating a barleycorn with a centimeter absurd. – Yitzchak Aug 25 '14 at 0:55
@Yitzchak, I just did the math based on Double AA's link and found that the Rambam's retzuot are ~8.5mm wide at the minimum, which is not far from the 9mm ruling that's often followed on less expensive retzuot. Of course, most are wider to account for stretching and more stringent opinions. – Noach MiFrankfurt Aug 5 '15 at 13:18

Minimally the retzuah must be 9mm wide. For Ashkenazim they should preferably be 11mm according the the Chazon Ish. 10mm width is sufficient for Sephardim.

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Can you source these lengths? – Double AA Sep 19 '12 at 19:10