מסכת כלים

פרק כז משנה י

שלשה על שלשה

Three by three (handbreadths of cloth that were tamei midras)

that was split

is tahor from midras

but is tamei for contact with something that was tamei midras (namely, itself).

Rabbi Yosi said,

"And why, with which midras did this come into contact with?

Rather, only if the zav touches it

it it tamei for contact for being in contact with the zav."

שלשה על שלשה

(that was found) in the trash heaps,

(will still be susceptible to tumah if it is) whole and can wrap up salt (otherwise, having been discarded, this material was shown to have no value, and loses its status as a utensil);

in a house,

(will still be susceptible to tumah if it is) either whole

or able to wrap up salt.

How much salt must one wrap up?

A quarter (of a kav);

Rabbi Yehuda says

of fine (salt),

and the Sages say

of coarse (salt);

both of them intend to be lenient. (Requiring the material to be of a stronger weave in order to be susceptible to tumah would be the more lenient position, and both sides of this dispute held that theirs required stronger material.  According to Rabbi Yehuda, a quarter-kav volume of fine salt is heavier, and so the the three by three piece of cloth would have to be stronger than that for coarse salt; the Sages hold that since coarse salt is rougher and more abrasive than the fine salt, the material used to wrap that quality of salt must be stronger.)

Rabbi Shimon says

they are equivalent,

three by three (handbreadths of cloth) in the trash heaps

to three by three (fingerbreadths of cloth) in a house (in that both are not susceptible to the tumah of midras, but are susceptible to other types of tumah).