Kelim, Chapter Twenty-Four, Mishnah Five
There are three different types of leather covers:
1) That of barbers is susceptible to midras uncleanness;
2) That on which people eat is susceptible to corpse uncleanness.
3) And that for [spreading out] olives is free from all uncleanness.
Section one: The leather cover that barbers use is meant to be sat upon, therefore it is susceptible to midras.
Section two: The leather cover people eat on is not meant for sitting but it is considered a vessel. Therefore, it is susceptible to corpse uncleanness.
Section three: The leather cover used to spread out olives isn’t even considered a vessel, and therefore it is pure