Kelim, Chapter Thirteen, Mishnah Four
1) An ash-shovel whose spoon was missing is still susceptible to impurity, since it is still like a hammer, the words of Rabbi Meir.
a) But the sages rule that it is clean.
2) A saw whose teeth are missing one in every two is clean.
a) But if a hasit length of consecutive teeth remained it is susceptible to impurity.
3) An adze, scalpel, plane, or drill that was damaged remains susceptible to impurity, but if its steel edge was missing it is clean.
4) In all these cases if it was split into two parts both remain susceptible to impurity, except for the drill.
5) The block of a plane by itself is clean.
Section one: The ash-shovel is used to rake out coals from an oven. According to Rabbi Meir even if the shovel was removed, it is still susceptible because its heavy iron body is still usable as a hammer. Although this was not its original use, it still has some use, this use is sufficient for it to remain susceptible. The other sages hold that since it can no longer be used for its original purpose, it is no longer susceptible to impurity.
Section two: If one out of every two teeth is missing, the saw is no longer susceptible to impurity, because with so many teeth missing, it is no longer usable. However, if a hasit (some say that this is the length between the forefinger and thumb and some say between the forefinger and middle finger) length of teeth remain in one place, then the saw is still usable and is still susceptible.
Section three: In general, these instruments remain usable and therefore susceptible to impurity even when damaged.
They would put a piece of steel in all of these instruments to strengthen and sharpen it. If this piece of steel was removed, then the instrument is no longer susceptible.
Section four: Except for the drill, all of these instruments are usable even if split in two. Therefore, they are all still susceptible. Since the drill is not usable when it is split in two, it is not susceptible.
Section five: The block of a plane whose steel edge has been removed is no longer usable and therefore it is clean.