Reference for Beitzah 2:9
הָרֵחַיִם שֶׁל פִּלְפְּלִין טְמֵאָה, מִשּׁוּם שְׁלשָׁה כֵלִים, מִשּׁוּם כְּלִי קִבּוּל, וּמִשּׁוּם כְּלִי מַתָּכוֹת, וּמִשּׁוּם כְּלִי כְבָרָה:
A pepper mill acquires uncleanliness by reason of three vessels. [If one of the parts separates, it is not regarded as a fragment of a vessel, which does not acquire uncleanliness), but each one is considered a vessel in itself and acquires uncleanliness, even though when they are on the mill they are connected and look like one vessel]: (It acquires uncleanliness) by reason of "a receptacle" [The lower part, which receives the pepper ground through the holes of the sieve, acquires uncleanliness by reason of "a receiving vessel," being a wooden vessel with a receiving element.]; and by reason of a metal vessel [The upper part, which crushes and grinds the pepper acquires uncleanliness by reason of "a metal vessel." It does not acquire uncleanliness as a wooden vessel (flat wooden vessels remaining clean), but because of its lower covering, which is of metal]; and by reason of "a sieving vessel." [The middle part, which surrounds the sieve, does not acquire uncleanliness as a wooden vessel, not being a receptacle. But the sages decreed that a sieve acquire uncleanliness by reason of a weaving vessel, so that even if the sieve if not of metal, it acquires uncleanliness by reason of "a sieving vessel."]