Mishnah for Oholot 13:1
הָעוֹשֶׂה מָאוֹר בַּתְּחִלָּה, שִׁעוּרוֹ מְלֹא מַקְדֵּחַ גָּדוֹל שֶׁל לִשְׁכָּה. שְׁיָרֵי הַמָּאוֹר, רוּם אֶצְבָּעַיִם עַל רֹחַב הַגּוּדָל. אֵלּוּ הֵן שְׁיָרֵי הַמָּאוֹר, חַלּוֹן שֶׁסְּתָמָהּ וְלֹא הִסְפִּיק לְגָמְרָהּ. חֲרָרוּהוּ מַיִם אוֹ שְׁרָצִים אוֹ שֶׁאֲכָלַתּוּ מַלַּחַת, שִׁעוּרוֹ מְלֹא אֶגְרוֹף. חָשַׁב עָלָיו לְתַשְׁמִישׁ, שִׁעוּרוֹ פוֹתֵחַ טֶפַח. לְמָאוֹר, שִׁעוּרוֹ מְלֹא מַקְדֵּחַ. הַסְּרִיגוֹת וְהָרְפָפוֹת מִצְטָרְפוֹת כִּמְלֹא מַקְדֵּחַ, כְּדִבְרֵי בֵית שַׁמַּאי. בֵּית הִלֵּל אוֹמְרִים, עַד שֶׁיְּהֵא בְמָקוֹם אֶחָד מְלֹא מַקְדֵּחַ. לְהָבִיא הַטֻּמְאָה וּלְהוֹצִיא הַטֻּמְאָה. רַבִּי שִׁמְעוֹן אוֹמֵר, לְהָבִיא הַטֻּמְאָה, אֲבָל לְהוֹצִיא אֶת הַטֻּמְאָה בְּפוֹתֵחַ טָפַח:
One who makes a skylight initially, its size [to spread impurity] is the thickness of the drill of the Temple chamber. The remainder of the skylight is two fingers high by a width of one thumb. What is the remainder of the skylight? A window which was closed up but not completely finished. If it was bored away by water or vermin or if salt corroded it, its size is a fistful. If he thought he would use it, its size is a handbreadth's space, if [he wanted it just] for light, its size is that of a large drill. Lattices and gratings combine to make the thickness of a drill according to Beit Shammai, but Beit Hillel say until there is in one place the thickness of a drill. [This size is enough] to spread impurity and to allow for impurity to exit. Rabbi Shimon says to spread impurity, but to allow for impurity to exit requires a handbreadth's space.