Keilim, Chapter 12, Mishnah 3. This chapter examines metal objects that are not complete keilim in the ordinary sense: pieces, parts and attachments. The question running through it is whether such an item has an identity of its own, which would make it susceptible to tumah, or whether it is merely a component of something else. The mishnah just before this one dealt with a hook fixed onto a keli and when it can receive tumah. Our mishnah continues with a series of similar items, each judged by the same standard: does it serve a purpose of its own, or is it swallowed up in the larger object (or in the ground) to which it belongs?
A teini and its lid
A teini was a basket of a fixed capacity, three kav, kept in the house. People used it to store scrap metal and the broken shards of earthenware keilim. Its cover was also made of metal, and it was formed with a certain depth, so that it was capable of holding things.
The mishnah rules: "Kisui teini shel matechet shel ba'alei batim, Rabban Gamliel metamei." When an ordinary householder's teini has a lid fashioned from metal, Rabban Gamliel holds that tumah can take hold of it, and that this is so even when the lid stands apart from the basket. Admittedly it bears no title of its own (one identifies it only by the basket it closes), yet in his view it is a full utensil: it was formed with a hollow, like any receptacle, and people did in fact place things inside it.
"Vachachamim metaharin," the Chachamim declare it tahor when it is separated from the teini. Although it is able to contain things, that is not what it is normally used for, and a capacity that is not put to use does not turn it into an independent keli.
"Veshel rofim tamei." When the teini belongs to a physician, its lid is susceptible to tumah, and here there is no argument. A doctor at work would regularly lay his remedies and his dressings in that lid while attending to the person before him. Because it was drawn into such service again and again, even the Chachamim grant it the standing of a utensil that can contract tumah.
The door of a cabinet
"Hadelet shebamigdal shel ba'alei batim tehorah." A wooden cabinet in an ordinary home may have its door fashioned from metal, and that door, taken by itself, does not receive tumah. Nothing identifies it independently; it is known only by the cabinet it belongs to, and by nothing further.
"Veshel rofim temei'ah." In a physician's cabinet, however, such a door is susceptible to tumah even on its own. A doctor would take it off and press it into service as a working surface, spreading his salve upon it and suspending his scissors from it. Regular use of that kind, independent of the cabinet, gives it the standing of a utensil in its own right.
Two kinds of tongs
The mishnah now turns to two instruments. The yitukin are tongs used to grip the small bowl, the crucible, in which silver is melted. The perachin are attached to a stove and are used to shift the pots standing inside it.
"Hayitukin temei'im," the yitukin are susceptible to tumah. They are metal keilim, and metal keilim receive tumah even though they form no receptacle at all.
"Vehaperachin tehorin." The perachin do not contract tumah. Their entire purpose lies in working together with the stove into which they are set, and that stove is fixed in the ground. Metal fastened to the ground lies beyond the reach of tumah, and these tongs share the status of the stove they serve.
The hook of the olive press and the hook in the wall
An akrav of a beit habad is a curved strip of metal fixed to the wooden beam of the press, used as a hook from which items are hung. "Akrav beit habad temei'ah": tumah can take hold of this hook. That holds true even though it is joined to a wooden beam, which is itself outside tumah since it forms no receptacle. The hook, though, has a job of its own. It never truly became part of the beam, and it was fastened there for one reason only: so that clothing and other objects could be suspended from it. Because it fills an independent role, it is subject to tumah.
"Ve'unkeli shebaktalim tehorah," a hook set into a wall is tahor. The wall belongs to the house, and the house is attached to the ground; the hook is therefore reckoned as part of the ground itself, and it cannot become tamei.
Read together, the cases of this mishnah trace one line: an item is judged a keli when its own use gives it standing, whether that use comes from the way it is shaped or from the trade of the person who owns it. Where the item is absorbed into a larger structure, and all the more so where that structure is fastened to the ground, it has no independent identity and remains tahor.