A covering that is a square, a handbreadth by a handbreadth and a handbreadth high brings ritual impurity and intervenes between ritual impurity according to Scriptural Law. For an ohel is given that distinction only when it is a handbreadth by a handbreadth and a handbreadth high or more.
What is implied? There was an olive-sized portion of a corpse lying with open space above it and implements (keilim), e.g., needles and spits, were at its side, without touching it. If one covered the portion of the corpse and the implements with an ohel that was a handbreadth by a handbreadth and was more than a handbreadth above the ground, the covering conveys impurity to the implements and renders them impure.
If there were other implements on top of this ohel that was a handbreadth by a handbreadth, they are pure, because the ohel intervenes between them and the impurity. Thus we have learnt that just as an ohel imparts impurity to everything that is under it, it preserves the purity of anything outside it, and intervenes between the impurity and the implements that are on top of it. Similarly, if the impurity was above the ohel and the implements were below it, the implements are pure, because the ohel intervenes in the face of impurity.
If the ohel was less than a handbreadth high or less than a handbreadth by a handbreadth, even if it was several handbreadths high, the implements that are next to the impurity are pure. Any of the implements that are above this ohel and are directly above the impurity are impure. The rationale is that they were positioned over the impurity and there was no ohel intervening in the face of the impurity. Similarly, if there was impurity above this ohel and implements beneath it, any implements that are directly beneath the impurity are impure, for the impurity was hanging over them and there is no ohel intervening in the face of the impurity. The rationale is that whenever there is less than a handbreadth of open space, it is considered as touching and the impurity under it is considered as "flush,⁠" as we explained.
When does the above apply? When the ohel was not a person or an implement. If, however, a person or an implement serves as an ohel over the impurity, whether they were the covering itself or the support for the covering, even if the implements were such that themselves do not contract impurity, they convey impurity and do not intervene in the face of impurity.
What is implied? If there was a board placed upon four men or on four implements, even stone implements or the like that do not contract impurity or, needless to say, if they were placed on four spits or four reeds that were a handbreadth high, and there was impurity and other implements beneath it, those implements are impure. If the implements were on top of the board, even if they were not directly above the impurity, they are impure. If there was impurity above the board and implements below it, all of the implements below the board are impure. If, however, the board was placed on four stones or on an animal or a beast and there was impurity under it, the implements on top of it are pure.

If there was impurity on top of a board, all of the implements under it are pure, because the ohel intervenes in the face of the impurity. Implements made from animal turds, stone implements, or implements made from earth that are oversized are considered as ohalim and not as implements. Therefore, they intervene in the face of impurity.

The following laws apply when a board was placed on top of a new oven and it protrudes beyond the oven on either side for more than a handbreadth. If there was impurity below the board, implements that are on top of it are pure. If there was impurity on top of it, the implements below it are pure. The rationale is that a new oven is not considered as a k'li in this context. If the oven was old, everything is impure.

When a board was placed over two ovens, even if they are old, and it protrudes beyond each oven and there is impurity below it, between the two ovens, only the space between them is impure. Keilim that are beneath the two ends that are beyond the ovens are pure, for the area beneath the ends and that beneath the ovens are considered as two tents, one next to the other.
Similarly, if a board was placed over an oven, even an old one, and it protruded a handbreadth at both ends, but not from the sides, should there be impurity under one end, keilim under the other end are not considered as impure.

The following laws apply when a person carries a k'li, e.g., a plow or the like, and one side of the k'li hung over impurity. If the circumference of the k'li was a handbreadth, even though its width was only a finger breadth and a third, it imparts impurity to the person carrying it. Impurity is conveyed to him according to Rabbinic Law, for our Sages decreed impurity for a k'li whose circumference is a handbreadth as a safeguard lest one be lenient when there is one whose width is a handbreadth. It does not, however, convey impurity to keilim that are below it or other people over which it hangs unless its width is a handbreadth.

Wooden coffins in which a corpse is placed are not considered as graves. Instead, if there is a handbreadth of empty space between the covering of the coffin and corpse, the cover is considered as an intervening substance and one who stands on the cover is considered as pure according to Scriptural Law. Nevertheless, although most coffins have an empty space of a handbreadth, since there are some which do not have such space, our Sages degreed that no coffin would be considered as an intervening substance. Thus one who walks on a coffin is considered as if he touched a corpse or a grave.

The following laws apply when a beam extended from one wall to another wall and there was impurity under it. If it was a handbreadth wide, it conveys impurity to everything under its entire span. Any keilim or persons under it are impure. This applies even if its width is not the same along the entire span and some portions are less than a handbreadth wide. The rationale is that these portions are considered as part of an ohel. If it is not a handbreadth wide, the impurity pierces through and ascends and pierces through and descends, as we explained.
How much must the circumference be for the board to have a width of a handbreadth? If it is round, three handbreadths. If it is square, four handbreadths.

When a barrel a se'ah in size was on its side in an open area, it does not convey impurity to everything under its entire expanse unless it is approximately four and half handbreadths in circumference. In this way, its upper portion will be a handbreadth and a half above the ground and there will be a portion of it, a handbreadth by a handbreadth a handbreadth above the ground. Accordingly, if it was suspended half a handbreadth above the ground and its circumference was three handbreadths, it conveys impurity.
Similarly, if there is a round pillar lying in an open space and resting on the earth, it does not convey impurity under its side unless it is 24 handbreadths in circumference. If it is not 24 handbreadths in circumference, the impurity pierces through and ascends and pierces through and descends. The reason that 24 handbreadths are required is that whenever there is a circumference of three, there is a width of one. Whenever there is a square, a handbreadth by a handbreadth, its diagonal will be a handbreadth and two fifths. Therefore if the pillar's circumference was 24 handbreadths, there is a little bit more than a handbreadth by a handbreadth that is a handbreadth high under its entire side. All of these calculations are approximations. This is its form.