A board is placed on top of an old oven and protrudes a handbreadth in two direc-tions, but not on the other sides. [If there is] tumah on this side, utensils that are on the other side remain tahor. R’ Yose declares [them] tamei. A b’tach does not spread tumah. If there is a ledge, R’ Eliezer says: It does not spread tumah. R’ Yehoshua says: We view the btach as if it is does not exist, and the ledge above it spreads tumah.

[There is] a shield of the leg of a crib that protrudes through [the ceiling of the lower story of] a house. If the hole is as big as a handbreadth, everything becomes tamei; and if not, we count the way we usually count for [tumah from] a corpse.