Shabbat 81A

מתני׳ עצם כדי לעשות תרווד. רבי יהודה אומר: כדי לעשות ממנו חף. זכוכית ⁠— כדי לגרור בה ראש הכרכר. צרור או אבן ⁠— כדי לזרוק בעוף. רבי אלעזר בר יעקב אומר: כדי לזרוק בבהמה.

Mishnah: The measure that determines liability for carrying out a bone is equivalent to that which is used to make a spoon. R' Yehuda says: In a measure equivalent to that which is used to make from it a key. The measure that determines liability for carrying out glass is equivalent to that which is used to scrape and smooth the top of a bobbin, a sharpened stick used by weavers. The measure that determines liability for carrying out a pebble or a stone is equivalent to that which is used to throw at a bird to chase it away. R' Elazar bar Ya’akov says: Equivalent to that which is used to throw at an animal, which is larger.

גמ׳ למימרא דשיעורא דרבי יהודה נפיש? הא קיימא לן דשיעורא דרבנן נפיש! אמר עולא: חפי פותחת. תנו רבנן: חפי פותחת טהורין, קבען בפותחת טמאין. ושל גל, אף על פי שחיברן בדלת וקבען במסמרים טהורין ⁠— שכל המחובר לקרקע הרי הוא כקרקע.

Talmud: The Talmud asks: Is that to say that the measure of R' Yehuda is greater? Don’t we maintain that the measure of the Rabbis is greater? Ulla said: R' Yehuda did not refer to the entire key, but to the teeth of a key. With regard to the above, the Talmud cites that which A baraita states: The teeth of a key are ritually pure, and they cannot become impure when separate from the key, as they have no function on their own. However, if one affixed them to a key, they can become ritually impure as part of a utensil. And teeth of a lock, even though one attached them to the door and affixed them with nails, are ritually pure, as anything attached to the ground has the same legal status as the ground itself, which cannot become ritually impure.