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מסכת כלים פרק יב משנה ו
ארבעה דברים [With regard to] four things
רבן גמליאל מטמא Rabban Gamliel ruled tamei
וחכמים מטהרין and the Sages ruled tahor:
כסוי טני של מתכת The metal cover of a teni (a type of metal box which is susceptible to tumah),
של בעלי בתים of householders (see 12:3),
ותלוי המגרדות and the hanger of strigils (A strigil was an metal instrument with a curved blade used to scrape sweat and dirt from the skin before bathing; it would be hung from a hook and Rabban Gamliel held the hook to be tamei since it would, even if only rarely, be moved),
וגלמי כלי מתכות and unfinished metal utensils (which Rabban Gamliel held to be tamei as they were sometimes used for their intended purposes in their unfinished state)
וטבלה שנחלקה לשנים and an [earthenware, rimmed] tray that was split into two [equal halves] (Rabban Gamliel rules that, as we cannot precisely determine which half is larger, both are tamei);
ומודים חכמים and the Sages concede
לרבן גמליאל to Rabban Gamliel
בטבלה שנחלקה לשנים by a tray that was broken in two,
אחד גדול ואחד קטן one large and one small
שהגדול טמא והקטן טהור that the large [fragment] is tamei and the small is tahor.
 

פרק יב משנה ז
דינר שנפסל A dinar that became unfit (either due to government rule or wear and tear)
והתקינו לתלותו בצואר קטנה and was prepared to hand around the neck of a young girl
טמא

is tamei (although coins are usually tahor, this one has become a piece of jewelry),
וכן סלע שנפסלה and similarly, a sela that became unfit
והתקינה להיות שוקל בה and was prepared to weigh with it (i.e. to be used as a weight on a balance scale)
טמאה is tamei.
עד כמה תפסל Until what point may it [a sela] be unfit
ויהא רשאי לקיימה and one is still allowed to keep it?
עד שני דינרין Until two dinars (half its original size),
פחות מכן יקוץ less than that he must cut it up (as otherwise it could be used to cheat. 

Note that "until two dinars" has two meanings: First, that a sela that weighs less than two dinars must be destroyed, and second that a sela that has eroded, until it has eroded half its weight, that is two dinars, it must be destroyed, as people might mistake it as being worth less than it is.  Consequently, a sela that has eroded must be destroyed unless it it worth exactly two dinars.)