Keilim, Chapter 13, Mishnah 4. This chapter follows metal tools through their life of wear and breakage, asking in each case whether what remains is still a keli that can receive tumah, or whether it has become nothing more than a piece of metal. Our mishnah brings a series of workman's tools: a fire shovel, a saw, a small ax, a scalpel, a plane and an auger, and it asks in each case how much damage a tool can absorb and still count as a utensil.
The Fire Shovel That Lost Its Scoop
To follow the first case, picture the tool. A magreifa, a fire shovel, has a handle with a flat scoop at its end, and precisely at the junction where the handle meets the scoop there sits a ball of metal.
So the mishnah teaches: "magreifa shenitla kapah, temei'ah, mipnei shehi kekurnas." Break off the scoop and the shovel still receives tumah, since it now has the look of a kurnas, a hammer. What stays in the hand is a shaft topped by a ball of metal, which is precisely how a smith's hammer is built. One use has fallen away, and a second use steps in immediately.
"Divrei Rabbi Meir." Such is the ruling of Rabbi Meir. As he sees it, the owner need take no formal step whatever. From the instant the scoop snaps away, the piece that survives already is a hammer, and no one doubts that from here on he will use it for hammering.
"Vachachamim metaharin." The Sages disagree and declare the broken shovel tahor. For them the tool has lost the purpose for which it was made, and that settles the question. True, the remnant could serve as a hammer, but that was never its original purpose, and its owner never designated it for that role. Absent such a designation, what we hold is a broken keli, and a broken keli does not receive tumah.
The Saw With Alternate Teeth Missing
"Megeirah shenitlu shineha achat mibeintayim, tehorah." Take a saw and pull out its teeth in alternation, one gone and one left, and it is pure. Teeth spaced that way will not bite into wood, and a saw that cannot saw has stopped being a keli. It sheds its tumah on its own from that moment.
"Nishtayeir bah melo hasit bimakom echad, temei'ah." Should one spot along the blade still hold a full row of teeth measuring a sit, tumah applies. And what is a sit? Spread the pointer finger away from the finger beside it, as in the familiar peace sign, and measure from the tip of the one to the tip of the other. Wherever on the blade such a stretch survives complete, with not a single tooth pulled from it, the saw in its entirety can become tamei, because that little run of teeth is enough to cut with. One working portion holds the whole tool inside the category of a keli.
Tools That Were Damaged
The mishnah turns now to four tools that are regularly battered in use. "Hama'asad" is a hatchet, wielded for splitting wood. "Veha'izmel" is a surgeon's knife. "Vehamafsalit" is a carpenter's plane: a block of wood holding a blade whose edge juts out below, which the craftsman runs back and forth across a board to shave it smooth. "Vehamachde'a" is a drill, an auger with a bent handle at its top for boring holes.
"Shenifgemu, temei'im." All of these, when damaged, remain susceptible to tumah, because they are still somewhat usable. The case is one where the handle was damaged while the cutting edge itself is still whole, and a tool whose working edge is intact remains a tool.
"Nital chisuman, tehorin." Strip away the sharp edge itself, however, and they become pure, for with the edge gone there is nothing left to work with.
Split in Two
"Vekulan shenechleku lishnayim, temei'im." Should one of these tools break apart into two pieces, the pieces go on receiving tumah, since a tool of this sort still does its job at half size. "Chuts min hamachde'a": the auger is the exception. Once it comes apart in two it is pure, because half an auger drills no hole and has no use left in it.
"Veharokni bifnei atzmah, tehorah." And if the blade of the plane is taken out, the wooden block left by itself is tahor, since on its own it serves no purpose whatsoever.
The thread running through the whole mishnah is a single question asked again and again: does what remains in the hand still do work? A handle with a metal ball, a saw with one good stretch of teeth, an ax with a damaged handle but a sound edge, half of a scalpel: these still function, and function is what makes a keli a keli. A saw whose teeth are gone, a tool whose edge has been removed, half an auger, a plane's block without its blade: these do nothing, and a tool that does nothing is beyond the reach of tumah.