פירוש על כלים 24:5

תרבוסים (dressers/counters) – leather vessels similar to chests.

There are three different types of leather covers:
That of barbers is susceptible to midras uncleanness; The leather cover that barbers use is meant to be sat upon, therefore it is susceptible to midras.

ספרים – who engage in blood letting.

That on which people eat is susceptible to corpse uncleanness. The leather cover people eat on is not meant for sitting but it is considered a vessel. Therefore, it is susceptible to corpse uncleanness.

טמא מדרס – it is large and appropriate for sitting or to mix wine upon it.וש

And that for [spreading out] olives is free from all uncleanness. The leather cover used to spread out olives isn't even considered a vessel, and therefore it is pure

שאוכלים עליו – it is a vessel of usage.

ושל זיתים – to press on it the olives. It is not considered a vessel for human usage.