Ohalot, Chapter Fourteen, Mishnah Three
1) A rod above a doorway, even if one hundred cubits higher, forms a passage for the uncleanness no matter its width, the words of Rabbi Joshua.
2) Rabbi Yohanan ben Nuri says: don’t be more stringent than the case of a projection.
Section one: The mishnah deals with a rod that was placed above a doorway, assumedly also to serve as some sort of protection for the entrance. The difference between the rod and the projection discussed in yesterday’s mishnah is that the projection is fixed into the wall of the house, whereas the rod can be moved. Therefore, according to Rabbi Joshua, it doesn’t matter how high the rod is, it always serves to bring impurity into the house. Rabbi Joshua holds that since it can be moved to within twelve handbreadths of the house (see mishnah one) we treat it as if it is within twelve handbreadths of the house.
Section two: Rabbi Yohanan ben Nuri says that the rule governing the rod should be no stricter than the rule governing the projection. Therefore, if the rod is more than twelve handbreadths high, it must be at least one handbreadth wide in order to bring impurity.