Kelim, Chapter Twenty-Four, Mishnah Two
There are three different types of wagons:
1) The one made like a cathedra is susceptible to midras uncleanness;
2) The one made like a bed is susceptible to corpse uncleanness,
3) And the one for [the transport of] stones is free from all uncleanness.
Section one: A “cathedra” is a seat upon which important people sit (see 22:3). If a wagon is made in such a manner it is considered a seat and it is susceptible to midras uncleanness.
Section two: A wagon made like a bed is used for transporting goods and it is not meant for people to sit or lie upon. Therefore, it is not susceptible to midras uncleanness. However, it is susceptible to corpse uncleanness.
Section three: A wagon used to transport large stones is made of boards placed upon the length and breadth of the wagon. There are large gaps between the boards such that it cannot hold in pomegranates. Therefore, it is not considered a vessel that can become impure. Rather, it is a simple wooden vessel (17:1) and simple wooden vessels are not susceptible to impurity.