Mishnayos Keilim Perek 25 Mishnah 2

מרדע (handle of the plough-having on one end a broad iron blade/חרחור and on the other a spud/דרבן) – It is a long, round staff that is a third of a handbreadth thick. And at its one end, is a wide piece of sharpened iron to sever/cut the roots, and its name is חרחור/broad iron blade, and its other end is a piece of iron like an awl/borer, whose name is דרבן /spud/point, through which leads the heifer to its furrow/ridge.

משבעה לחרחור מארבעה לדרבן – if impure liquids fell upon the broad iron blade, it is not impure from the handle of the plough other than seven handbreadths, but if they fell on the spud/point, it is not impure other than four-handbreadths. But Maimonides explained/expounded, that if if impure liquids fell on the handle of the plough seven handbreadths outside from the broad iron blade or outside four handbreadths from the spuds, it is like a vessel whose outsides had been defiled, but its inside was not defiled, and those seven handbreadths that are next to the broad iron blade and the four [handbreadths] that are next to the spud were not defiled.

אלא לשיריים – when the Sages gave measurements for the broad iron blade of seven [handbreadths] and for the spud four [handbreadths], it was not given other than regarding this matter that if the handle of the plough was broken and there remained next to/adjacent to the broad iron blade seven handbreadths, or adjacent to the spud four [handbreadths, it is impure, because it is appropriate to do some kind of its work. Less than this, it is like the shards of a vessel and is pure. But the Halakha is according to Rabbi Yehuda.