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.

The joists of the lower and upper stories of a house have no plaster attached to them and are perfectly aligned one above the other. If there is tumah underneath one of [the joists], [whatever is] beneath it becomes tamei. [If there is tumah] be-tween the lower and upper [joists], whatever is between them becomes tamei. [If there is tumah] above the upper [joist], whatever is directly above it, until the sky, becomes tamei. If the upper [joists] correspond to the space between the lower ones, [and] there is tumah under one [of the joists], whatever is beneath any of them becomes tamei. [If the tumah is] above them, whatever is directly above it, until the sky, be-comes tamei.

[In the case of] a beam that was placed from one wall to another [and] there is tu-mah underneath it: if there is a handbreadth, [it] spreads tumah underneath its en-tirety. If not, tumah penetrates upward and downward. How large a perimeter will have a width of a handbreadth? If [the beam] is round, its perimeter must be three handbreadths. If it is square, [its perimeter must be] four [handbreadths]; because a square exceeds a circle by one quarter.

[In the case of] a pillar lying [on its side] outdoors, if its circumference is twenty-four handbreadths, tumah spreads under its side. If not, tumah penetrates upward and downward.

[If] an olive-sized piece of corpse adheres to a threshold, R’ Eliezer considers the house tamei; [whereas] R’ Yehoshua declares it tahor. [If the piece of corpse] is lo-cated below the threshold, it is ruled half and half. [If it] adheres to the lintel, the house becomes tamei. R’ Yose declares it tahor. [If the piece of corpse] is located inside the house, someone who touches the lintel becomes tamei. [If] someone touches the threshold, R’ Eliezer considers [him] tamei. R’ Yehoshua says: From a handbreadth and below, he remains tahor; from a handbreadth and above, he becomes tamei.

If a new window is made for light, its size [to spread tumah] is the large gimlet of the [Temple] chamber. If some of the window is left, [the size] is the height of two fingerbreadths by the width of a thumb. What are cases in which ‘‘some of the window is left’’? A window was being boarded up, but the job was not completed. The minimum size for a hole created by erosion through water, small animals, or salt is the size of a fist. If someone decided to use [this hole] for general usage, its size is a square handbreadth; if for light, the size of a gimlet. Lattices and screens combine to equal the size of a gimlet according to Beis Shammai. Beis Hillel say: Only when the size of a gimlet is in one place. [The above list establishes the criteria] to allow tumah to enter and to allow tumah to exit. R’ Shimon says: [These are the minimum dimensions] to allow tumah to enter, but to allow tumah to exit [the minimum amount is] a square handbreadth.

The minimum size of an exterior window is the size of a gimlet. [If] a house was built outside it, the size [of the window] is a square hand-breadth. If the ceiling was placed in the middle of the window, the [size of the] lower part is a square handbreadth, and the upper part, a gimlet.

A hole in the door should be measured with the size of a fist; these are the words of R’ Akiva. R’ Tarfon says: [This hole is measured] with a square handbreadth. [If] the carpenter left a space at the bottom or top, or he did not complete [the door], or the wind opened [the door], [the hole] is measured with the size of a fist.

There is no minimum size [for a hole] that is made for a stick, a ‘‘sword,’’ or a lamp, according to Beis Shammai. Beis Hillel say: A square handbreadth. [If a hole was made] to be a peephole, to speak with his friend, or for other usage, the minimum size is a square handbreadth.

The following items reduce the [opening to less than a] handbreadth: Less than an olive-sized piece of flesh reduces [the opening if the source of tumah] is a quarter [of a kav] of bone; a piece of bone smaller than a barleycorn reduces [the opening if the source of tumah] is an olive-sized piece of corpse flesh; less than an olive-sized piece of corpse flesh; less than an olive-sized piece of carcass; less than a lentil-sized piece of sheretz; less than an egg-sized piece of food; grain [covering] the window; a thick spider web; the carcass of a kosher species of bird that was not designated [for food]; the carcass of a nonkosher species of bird that was designated [for food] but was not rendered capable of contracting tumah, or it was rendered capable of contracting tumah but was not designated [for food].

The following items do not reduce [the opening to less than a handbreadth]: Bone does not reduce if [the source of tumah is] bone; flesh does not [reduce] if [the source of tumah is] flesh; an olive-sized piece of corpse flesh does not [reduce the opening]; an olive-sized piece of carcass does not; a lentil-sized piece of sheretz does not; an eggsized piece of food does not; grain [growing] in the window does not; a very thin spiderweb does not; the carcass of a kosher species of bird that was designated [for food] does not; the carcass of a nonkosher species of bird that was designated [for food] and was ren-dered capable of contracting tumah does not; warp and woof threads that have con-tracted tzaraas do not. Also a brick made from a beis hapras does not; these are the words of R’ Meir. The Sages say: The brick reduces [the opening], because its earth is tahor. This is the rule: Anything that is tahor reduces [the opening], and anything that is tamei does not reduce [the opening].

A ziz-type ledge conveys tumah even if its width is minimal; whereas gizrah- and gavlis-type ledges [convey tumah] only if they are a handbreadth wide. What is a ziz-type ledge? [A ledge] whose face extends downward. And [what is] a gizrah-type ledge? One whose face extends upward. When does a ziz-type ledge convey tumah even if its width is minimal? When the ledge is three rows of stones, which is twelve handbreadths, above the doorway. [If the ledge] is higher, it spreads tumah only if it is a handbreadth wide. Ornamental archways and awnings spread tumah if they are a handbreadth wide.