Keilim, Chapter 14, Mishnah 1. This mishnah picks up the subject that the previous chapter was engaged in: a metal keli that has broken. The question is always the same one: is what remains in our hands still a keli, something that can become tamei, or is it now nothing more than a piece of metal?
The governing rule for metal is this: as long as the broken keli can still perform some part of the work it was originally made to do, it remains a keli and it can become tamei. But once it can no longer do its normal job, it is no longer a keli, and this is true even if the remnant is genuinely useful for something else.
Here lies the sharp difference between metal on the one hand and wood and earthenware on the other. A wooden or earthenware keli that broke can still become tamei if the remaining piece serves any useful purpose at all, whatever that purpose may be. A metal keli is judged more strictly: it must still serve its own purpose. Our mishnah now takes that principle and applies it, keli by keli, giving us the minimum measure that must be left in each case.
The question of the mishnah
The mishnah begins with a question: "Klei matachot, kama hu shiuran?" Metal kelim, what is their measure? That is to say: when such a keli has broken, what portion of it must survive in order for tumah still to take hold of it?
The bucket and the kettle
"Hadeli, kedei limlot bo": a bucket, enough to draw water with it. We are speaking of a metal bucket that broke. As long as what is left can still be used to draw water, it is a bucket and it can become tamei. If less than that remains, so that drawing water with it is no longer possible, it is no longer a bucket at all.
"Kumkum, kedei leyachem bo": a kettle, enough to heat water in it. The measure for a broken kettle is that it must still be able to do the work of a kettle, namely to heat up water inside it.
The urn and the lefes
"Mecham, kedei lekabel sela'im": a mecham, a sizeable water heater, must be able to contain sela coins. The required remnant here is smaller than what would be needed for heating water, since a mecham did not serve for heating alone. There were times when sela coins were stored inside it. Therefore, so long as what is left can hold sela coins, it is still carrying out one of the mecham's own functions, and it remains subject to tumah.
"Halefes, kedei lekabel kitoniyot": the lefes, enough to hold small jugs. A lefes is a very large pot that was filled with boiling water, and kelim were washed inside it. Its measure is that it must be able to hold the small jugs that were placed in it.
"Kitoniyot, kedei lekabel perutot": those small jugs themselves, enough to hold peruta coins. Again the same logic: small jugs were at times used to store perutot, so a broken jug that can still hold perutot is still functioning as a jug.
Measuring vessels
"Midot yayin beyayin, umidot shemen beshemen": wine measures are judged by wine, and oil measures are judged by oil. A vessel made for measuring wine can become tamei only so long as it is still fit to measure wine, and a vessel made for measuring oil only so long as it is still fit to measure oil. Their function is measuring, and that function is the standard by which the remnant is judged.
The view of Rabbi Eliezer
"Rabbi Eliezer omer: kulan biperutot." Rabbi Eliezer disagrees regarding the measuring vessels. In his opinion all of them, every measuring vessel, are judged by whether they can hold peruta coins. If the broken remnant is large enough to hold perutot, it can become tamei, even though it is no longer fit for measuring wine or oil. His reasoning is that measuring vessels of every kind were also used from time to time to store perutot, and that too is one of their uses.
So the mishnah has given us a whole shelf of broken metal kelim: bucket, kettle, urn, lefes, small jugs and measures. In each case we do not ask whether the broken piece is useful, but whether it can still do the work for which it was made.