Keilim, Chapter 13, Mishnah 5. This mishnah continues the chapter's discussion of metal utensils that have become broken or damaged, and asks in each case whether enough usefulness remains for the object to still count as a keli that can receive tum'ah. The subject here is metal needles.
A metal needle normally has two working parts. There is the ayin, the eye, the opening through which the thread is passed, and there is the uktz, the point, which is what pierces the material, for example a garment that is being sewn.
The sewing needle
The Mishnah begins: "Machat shenitla charirah o uktzah, tehorah." A sewing needle whose eye was removed, or whose point was removed, is tahor. Once either part is gone the needle can no longer perform the work of sewing, and an object that cannot do its job is no longer a keli at all, so it does not receive tum'ah.
Yet such a needle can be given a second career. The Mishnah adds: "Im hitkinah lemituach, teme'ah." If its owner fitted it out and set it aside for pulling fabric taut, it becomes susceptible to tum'ah once more. That particular job can be done by a needle that has neither a threading hole nor a genuinely sharp tip. The practice was to take four such needles and drive them through the four corners of a garment that had to be spread out and held tight, anchoring them into a board. No thread passes through anything, and no fine point is required. Since the object really does serve this function, halachah treats it as a keli.
The sackmaker's needle
Having dealt with an ordinary sewing needle, the Mishnah turns to the needle used by those who manufacture sacks. Sacks are made from coarse, very thick cloth, so the needle used for them is correspondingly broader and heavier than a regular needle.
Concerning it the Mishnah rules: "Shel sakin shenitla charirah, teme'ah." Should this needle lose its eye, it nevertheless remains susceptible to tum'ah, and the reason is given: "mipnei shehu kotev bah," a person is able to write with it. Admittedly, with the eye gone there is no way to thread it and sewing sacks is out of the question, but its breadth and thickness let it serve as a writing tool, and that one surviving use preserves its standing as a keli.
"Nitla uktzah, tehorah." If instead the point was removed, it is tahor. Without a tip it cannot sew, and it also cannot be used for writing, so nothing useful is left of it.
The stretching needle
Next comes the needle that was produced from the start for the job of pulling fabric taut. Of this one the Mishnah says "shel mituach," and rules "bein kach uvein kach," in the one case as in the other, "teme'ah": it is susceptible whether what it lost was its eye, or its tip, or both together. The reasoning matches what was said earlier about an ordinary needle fitted out for this purpose. Spreading cloth tight calls for no threading hole and no piercing point, so their absence costs the needle nothing of its work, and it keeps the status of a keli.
A rusted needle
"Machat shehe'alta chaludah": a sewing needle that has grown rusty. Here everything turns on how far the corrosion has gone. Where the rust gets in the way of the sewing, "im me'akevet et hatefirah," the needle is tahor, for its usefulness has been lost. Where the sewing is unhindered, "ve'im lav," the ruling is "teme'ah," it remains susceptible to tum'ah, since it goes on doing precisely what it always did.
The small roasting fork
The Mishnah closes with a small fork whose prongs are curved. Such a fork was used for roasting meat, and its teeth were bent precisely so that they could grip the meat or whatever else was being held over the fire.
"Tzinorah shepishtah, tehorah." A small fork whose curved prongs were straightened out is tahor, because in that state it can no longer hold anything and is no longer usable.
"Kefafah, chazrah letum'atah." If the owner bent the prongs back into their original curved shape, the fork returns to its tum'ah. In other words, if the fork had been tamei and then lost that tum'ah when the prongs were straightened and it ceased to be a keli, once the prongs are restored to their proper curve it is a keli again and once again receives tum'ah.
Running through the whole mishnah is a single principle: tum'ah attaches to an object only as long as it can still do work for a person. Remove the eye and the point and a sewing needle is a piece of metal; restore a purpose, whether stretching cloth, writing, or gripping meat, and the very same piece of metal is a keli once more.