Kelim, Chapter Twenty-Five, Mishnah Two
1) An ox-goad has different laws for its outer and inner parts,
a) [The outer part is] the seven handbreadths from the broad blade and four handbreadths from the point, the words of Rabbi Judah.
2) Rabbi Meir says: it is not to [subject to such distinction], the four and the seven handbreadths were mentioned only in regard to its remnants.
Section one: An ox-goad is the stick which was used to drive the oxen (to goad them on). On one end was a point. The other end was a broad piece of iron that was also used for plowing and for cleaning the dirt off the plow. According to Rabbi Judah beyond seven handbreadths on the piece of iron and four handbreadths on the point is considered the outer part of the ox-goad. If impure liquids come into contact with the ox-goad beyond these two points, the “inner” part of the ox-goad remains pure.
Section two: Rabbi Meir again disagrees and holds that there is no “inner” or “outer” portion for an ox-goad. He does admit that the numbers four and seven handbreadths were mentioned by earlier generations of sages. But he holds that these numbers were mentioned with regard to the remnants of an ox-goad, not with regard to the “inner” or “outer” sides. According to Rabbi Meir, if seven handbreadths of the blade or four handbreadths of the point remain, the ox-goad is still impure (or susceptible to impurity). Less than that and the ox-goad is pure.