Keilim, Chapter 21, Mishnah 3. This chapter examines a practical question that comes up constantly with working tools: when a person touches one part of a tool whose other part is tamei, does the tumah travel to him? A tool is often an assembly of several pieces, and the Mishnah teaches us to distinguish between a piece that is genuinely a component of the utensil and a piece that merely sits alongside it, held in place loosely for as long as the work is being done. Our mishnah applies that distinction to a carpenter's saw, a press, a drill, a bow and a trap.
The bow saw and its handles
The tool under discussion is the megerah, a bow saw. Its cutting element is a long blade, and the craftsman grips it with both hands, one at each end, sliding the blade back and forth through the wood.
The Mishnah begins: "Hanogea beyad megerah mikan umikan, tamei." If the blade of the bow saw is tamei and a person takes hold of the handles set at either end of it, he becomes tamei. Those handles are not accessories lying near the blade; they are part of the utensil itself, the very place where a person is meant to hold it. Touching them is like touching the saw.
The parts that are only loosely attached
The Mishnah then lists parts of the same saw, and other tools as well, where the ruling is different: "Bachut uvameshichah, ba'amah uvahasenifin, bamachbesh shel charash, uvakashtanit, tahor."
- Hachut vehameshichah: the cord or band fastened along the upper portion of the saw, which holds the whole frame under tension.
- Ha'amah: the bar of wood that runs the length of the saw, bridging its two ends.
- Hasenifin: the piece of wood used to twist and tighten that cord, so that the blade is drawn taut.
- Machbesh shel charash: the carpenter's press. A board would be placed between its planks and the screw turned down, pressing the board flat and straightening it. Here a person touches the planks of the press while the screw itself is tamei.
- Kashtanit: an auger, the forerunner of our drill. A bit or blade is fitted into a handle, and the craftsman turns the bent handle around so that the bit bores a hole.
In every one of these cases the person who touches these pieces remains tahor, even though what he is touching is joined to a part that carries tumah. The reason is the nature of the joining: these pieces are held together loosely, fitted and tightened for the duration of the job and then released. They are not permanently fixed in place, and a piece that is only temporarily set against the tool is not reckoned as a component of that tool. For purposes of tumah, they remain separate objects.
Rebbi Yehudah on the frame of the large saw
"Rebbi Yehudah omer: af hanogea bamalben shel masor hagadol tahor." Rebbi Yehudah adds a case to the list: one who touches the wooden frame of the large saw is likewise tahor, even when the blade itself is tamei. His reasoning follows the same principle. The frame is not permanently bonded to the blade, so the two are not treated as a single entity where tumah is concerned.
The bow and the bowstring
"Hanogea bayeter uvakeshet, af al pi shehi metuchah, tahor." Picture an archer who has fitted a tamei arrow onto his bow and pulled the string back. A second person now lays his hand on the string, or on the wood of the bow itself. He remains tahor. At that moment the two objects are indeed pressed one against the other and are clearly serving a single purpose, yet they were never fastened together. Being in contact, even deliberate contact under tension, is not the same as being attached, and two items that come together only while a task is being carried out are not counted as one body with regard to tumah.
The mole trap
"Mesodat ha'ishut tehorah." A trap built to catch moles remains tahor. Inside it lies a shaft, the arrow that snaps at the animal when the trap is triggered. Should that shaft contract tumah, the trap is unaffected, because the shaft is not reckoned among the trap's own components, and so tumah has no route from it into the trap.
Rebbi Yehudah rules otherwise: "kol zman shehi metuchah, chibur." For as long as the cord is stretched tight with the shaft lodged in it, he treats the two as connected, so that tumah in the shaft carries over to the trap. In his understanding, a shaft set into a sprung trap is gripped tightly and held under real pressure precisely so that the trap will do its work, and a bond of that strength is enough to make the two into a single object.
The thread running through the entire mishnah is therefore one measure applied again and again: is this piece fixed into the utensil, or is it simply resting against it for the moment? The saw's handles are the utensil; its cord, bar and tightening peg are not. The bow does not become one with the arrow it launches. And regarding the mole trap, Rebbi Yehudah teaches us that when a part is held fast under tension in the working of the tool, that tension itself can be enough to make them one.