Reference for Kelim 20:7
מַחֲצֶלֶת שֶׁעָשָׂה לָהּ קָנִים לְאָרְכָּהּ, טְהוֹרָה. וַחֲכָמִים אוֹמְרִים, עַד שֶׁיַּעֲשֶׂה כְמִין כִי. עֲשָׂאָם לְרָחְבָּהּ וְאֵין בֵּין קָנֶה לַחֲבֵרוֹ אַרְבָּעָה טְפָחִים, טָהוֹר. נֶחְלְקָה לְרָחְבָּהּ, רַבִּי יְהוּדָה מְטַהֵר. וְכֵן הַמַּתִּיר רָאשֵׁי הַמַּעֲדַנִּין, טְהוֹרָה. נֶחְלְקָה לְאָרְכָּהּ וְנִשְׁתַּיְּרוּ בָהּ שְׁלֹשָׁה מַעֲדַנִּים שֶׁל שִׁשָּׁה טְפָחִים, טְמֵאָה. מַחֲצֶלֶת, מֵאֵימָתַי מְקַבֶּלֶת טֻמְאָה. מִשֶּׁתִּקָּנֵב, וְהִיא גְמַר מְלַאכְתָּהּ:
A mat in which reeds are run lengthwise is not susceptible to impurity. The Sages say, only if they are in the form of [the Greek letter] chi. If they were run through its width and there were not four <em>tefachim</em> [handbreadths] between each reed, it is not susceptible to impurity. If it were divided along its width, Rabbi Yehuda [says] it is not susceptible to impurity. So, too, if the end knots [of reed matting] are untied, it is not susceptible to impurity. If it were divided along its length, and three knots of six <em>tefachim</em> were left on it, it is susceptible to impurity. A mat - when does it become susceptible to impurity? When it is trimmed, as this completes its production.