Ohalos 2:4

The coffin lid and sides* convey impurity through contact and a tent but not through carrying; Rabbi Eliezer says they also convey impurity through carrying. Rabbi Yehoshua says that if there’s grave dust beneath them, they convey impurity through carrying; if not, then not. The sides are that which support the lid but the supports to the supports are ritually clean.

Ohalos 2:5

The following are ritually clean if they are any amount short of their requisite volumes: An olive-sized piece of a corpse, an olive-sized piece of dissolved flesh, a scoop of decomposed corpse, a reviis (about 3 oz.) of blood, a barleycorn-sized bone, and the limb of a living person, the bone of which is incomplete.

*There are different interpretations as to the meaning of goleil and dofeik. Another interpretation is that it refers to the headstone and the stones that support it.