Keilim, Chapter 11, Mishnah 4. The background to this mishnah is a rabbinic decree: a newly formed metal keli is declared tameh out of concern that the metal it was made from came from old kelim that were themselves tameh. Our mishnah asks how that decree operates when the new keli was not produced from one single source, but from a mixture of materials, and it then returns to a series of metal parts of a door and their status.
Iron mixed with iron
The first case is iron blended with iron: "barzel tameh," iron that bears tumah, "shebilalo im barzel tahor," which was mixed together with iron that is tahor. The two were melted down and a fresh utensil was cast from the combined metal. What decides the matter is which portion predominates. "Im rov min hatameh": when the larger share of the metal originated in the material that was tameh, the finished utensil is treated as tameh. "Ve'im rov min hatahor": when the larger share came from the material that was tahor, the utensil is tahor.
And what if neither side predominates? "Mechetza lemechetza, tameh": an even split leaves us with a utensil that is tameh. The Chachamim stretched their ruling to cover metal of which only half originated in used vessels, and their reason was protective. Had they declared such a utensil tahor, people were apt to lose hold of the distinction and imagine that metal drawn mostly from used vessels also yields something tahor. By folding the even split into the decree, they kept the decree from unraveling.
Clay mixed with dung
Majority governs a second case built of altogether different materials: "vechen min hachalma umin hagelalim." The word chalma refers to a clay-like earth; here it was worked together with cattle dung, shaped into a vessel and baked in the kiln. Dung can never bear the status of a keli, whereas clay can. Hence, when the dung predominates, what emerges is not reckoned a vessel at all and tumah has nothing to take hold of. When the chalma predominates, the product is a genuine keli and is susceptible. And where the two were used in equal measure, it can receive tumah.
The kelostera
Now the mishnah returns to the decree on metal: "kelostera teme'ah." A kelostera is a metal bolt or stopper used to hold a door shut, and this one has a knob on it by which it can be picked up. It is tameh, because of the very same concern that the metal from which it was formed may have come from kelim that were tameh.
This requires a clarification. Earlier in this chapter we learned that a door bolt is not susceptible to tumah, since it serves the door and the door is attached to the ground, and whatever serves the ground does not receive tumah. Here, however, the knob changes the picture. A bolt fitted with a knob is sometimes put to a second use, as an implement for crushing and grinding spices, and that use has nothing to do with the ground. Because it functions as an independent utensil in its own right, it can become tameh.
"Umesupah, tehorah." Suppose the body of the bolt was formed of metal about which there is no suspicion, and only its outer surface was coated with a layer of metal that may have come from vessels that were tameh: the bolt stays tahor. What decides a vessel's standing is the material of which it essentially consists, its principal substance, and that substance here is tahor. A coating is no more than secondary and carries no weight in the ruling.
The pin and the bolt socket
The mishnah continues with two further metal fittings of a door: "hapin vehapurnah teme'in." The pin and the purnah, made from metal that may have come from tameh kelim, are both tameh. Each one becomes tameh from the moment it is finished, even before it has been joined to its counterpart, because they are regarded as two distinct kelim. True, the pin and the bolt piece work in tandem to fasten and lock the door, yet since each has its own independent function, each one receives tumah on its own account.
The knobbed bolt on Shabbat
The mishnah closes with a disagreement over this very knobbed bolt, now approached from the angle of Shabbat. Picture the bolt fastened to the door by a length of rope. Rabbi Yehoshua rules: "shomtah mipetach zeh," one may slide it off this entrance, "vetolah bachavero beShabbat," and hang it on a different entrance on Shabbat, provided that he manipulates it by means of the rope and does not lift it in his hands. In his understanding the knobbed bolt does not qualify as a vessel, which makes it muktzeh, and muktzeh may not be carried about. Even so, as with other muktzeh objects, shifting something indirectly, tiltul min hatzad, is permitted, and so one moves it by pulling on the rope attached to it.
"Rabbi Tarfon omer, harei hi kechol hakelim, umitaltelet bechatzer." Rabbi Tarfon disagrees. To him it is a keli like any other keli, it is not muktzeh at all, and it may therefore be handled directly and moved about inside the house or the courtyard. His limitation is a different one: it may be moved within the courtyard but not out into the street, since one may not carry from a reshut hayachid to a reshut harabbim or from a reshut harabbim into a reshut hayachid. In short, according to Rabbi Tarfon the knobbed bolt has the full status of a keli and is free to be moved; one simply may not carry it outside.