Ohalos 12:3-4

Ohalos 12:3

If a board was laid across the mouth of an old oven and it protruded a handbreadth in either direction but not to the sides, then if there’s ritual impurity under one end of the board, utensils under the other end remain clean, though Rabbi Yosi rules them unclean. A windowsill doesn’t convey impurity; Rabbi Eliezer says not even if it has a projection. Rabbi Yehoshua says we consider the windowsill as if it’s not there and the upper projection conveys impurity.

Ohalos 12:4

Regarding the “sandals” placed on the legs of a cradle, if they wore a hole into the house (i.e., from an upper level), then if the hole is a handbreadth, everything is rendered unclean. If it isn’t a handbreadth, then we count degrees of impurity from it like we do from a corpse.