Kelim, Chapter Thirteen, Mishnah Eight
The final mishnah of chapter thirteen deals with various types of combs that have their teeth missing.
1) A flax-comb: if the teeth were missing but two remained, it is still susceptible to impurity.
a) If only one remained it is clean.
2) As regards all the teeth, each one individually is susceptible to impurity.
3) A wool-comb: if one tooth out of every two is missing it is clean.
a) If three consecutive teeth remained, it is susceptible to impurity.
b) If the outermost tooth was one of them, the comb is clean.
4) If two teeth were removed from the comb and made into a pair of tweezers, they are susceptible to impurity.
a) Even if only one was removed but it was adapted to be used for a lamp or as a stretching-pin, it is susceptible to impurity.
Section one: As long as two teeth of the flax-comb remained, the comb is somewhat usable and is therefore susceptible to impurity. If only one tooth remains, it is useless and therefore clean.
Section two: According to the Tosefta one can use the teeth of this type of comb as a writing instrument, and therefore if they are separated from the comb they can still become impure.
Section three: The rules governing a wool-comb are slightly different. If one out of every two teeth is missing, it is not usable and it is clean. But if three remain in one place, it can be used so it is susceptible, but only if the outer, wider tooth is not one of them. Since this tooth can’t be used for combing, it doesn’t count for the requisite three.
Section four: As was the case with the flax-comb, it is possible for the teeth to be removed and put to secondary use. Thus, if one uses the teeth of the wool-comb as tweezers, they are susceptible. And even a single tooth can be impure if it is removed and fixed to be used for a candle (to trim the wick) or for a stretching pin (see above, mishnah five).