Keilim, Chapter 17, Mishnah 12. This mishnah continues the chapter's discussion of the units of measure that the chachamim used throughout halachah. Many of these units are named after everyday objects, and everyday objects come in different sizes. So the Mishnah tells us which ones the chachamim intended in the larger version. The opening words are "v'yesh she'amru b'midah gassah": there are measures that the Sages stated in the coarse, that is, the larger, form. Whenever one of the following items appears as a shiur, picture the big one, not the small or average one.
A ladle of corpse dust
"Melo tirvad rakav." A corpse that has decomposed entirely turns into dust, and that dust is called rakav. A ladleful of it transmits tum'ah in an ohel, that is, to anything under the same roof. But how large is the ladle? The Mishnah answers: "k'melo tarvad gadol shel rof'im", the full measure of the large ladle used by doctors. Physicians would scoop out the ingredients of their medicines with such ladles, and their capacity was equal to what an average person can hold in his two cupped hands. That is the amount of corpse dust which conveys tum'ah in a tent.
The split bean of nega'im
"U'gris nega'im." The minimum size of a spot of tzara'at on the skin is a gris, a split bean. Here too the Mishnah specifies which bean: "k'gris hakilki", the split bean of Cilicia, a place whose beans grew unusually large. So the shiur of a nega is set by the bigger variety of bean, not by an ordinary one.
The large date of Yom Hakippurim
"Ha'ochel b'Yom Hakippurim k'koteves hagassah." One who eats on Yom Kippur is liable only if he eats the volume of a date, and again the Mishnah insists on the large date. This date is smaller than an egg, but it belongs to the large type.
The Mishnah then adds a precise detail: "kamoha v'chegar'inatah", the measure is the date together with its pit. Now, a date as it appears from the outside is actually bigger than that, because inside the fruit there is a small empty space between the flesh and the pit. That air is not part of the shiur. Only the fruit itself and the pit are counted, not the gap between them. Practically, to arrive at the exact measure one would first press the date together so that the internal space is squeezed out, and what remains is the volume that renders a person liable.
The wine and oil skins
"V'nodot yayin v'shemen, shi'uran k'fikah gedolah shelahen." A nod is a skin bottle used for holding wine or oil. Any keli loses its tum'ah once it has been damaged badly enough that it can no longer do the job it was made for, and here the Mishnah tells us how wide a tear in such a bottle must be before that happens: it is gauged by the large pikah, the ball, that belongs to these skins.
And what is that ball? A rounded ball would be set inside the skin, the leather then drawn up around it and tied off, leaving a little sack with the ball inside it protruding from the bottom of the bottle, and this sack served as a grip for carrying. Should the leather rip so widely that a ball of that sort would drop straight through, nothing further can be done with the bottle: it has ceased to be a keli, and tum'ah no longer applies to it. A narrower tear still leaves the pouch repairable, so the vessel retains its status and stays tamei. And the ball we measure by is the larger of the balls used with these wine and oil skins.
A gap in the wall that no one made
"U'ma'or shelo na'asah bidei adam, shi'uro k'melo egrof gadol." We are speaking of a corpse lying in one room, and an opening in the wall between that room and the next. If the opening is large enough, the tum'ah passes through it and the neighboring room becomes tamei as well. When the opening came about on its own and was not made deliberately by a person, the shiur is the fullness of a large fist.
Whose fist? The Mishnah supplies the name: "zehu egrofo shel Ben Batiach", the hand that belonged to Ben Batiach, a figure of the era of the Mishnah whose fist was legendary for its size. Rebbi Yose offers an image to convey it: "yeshno k'rosh gadol shel adam", his fist matched the dimensions of a big human head.
The opening that was made by a person
Until now we have been dealing with an opening that simply happened to be there. Now the Mishnah turns to a window that a person deliberately made in the wall in order to let in light. "V'shena'asah bidei adam, shi'uro k'melo makde'ach gadol shel lishkah." Since the opening was intended, a far smaller hole suffices to carry the tum'ah from room to room: the size of the hole bored by the large drill kept in the chamber of the Beit Hamikdash.
The Mishnah gives three familiar equivalents for that size: "shehu k'fundeyon ha'italki", the Italian fundeyon coin; "u'k'sela haneironis", the sela coin of Nero; "u'k'melo nekev sheba'ol", the hole in a yoke, meaning the hole drilled for the peg that fastens the yoke's ropes. An opening of that size in a man made window is enough for the tum'ah of the corpse to pass from the one room into the other.