There are three boxes: [Regarding] a worn-out [box] that one patched onto a sound one, we follow [the status of] the sound one. [If one patched] a small [box] onto a large one, we follow [the status of] the large one. [If] they were equal, we follow [the status of] the interior [box]. R’ Shimon says: [Regarding] the pan of a balance scale that one patched onto the bottom of a boiler, [if he patched it] on the inner surface [of the boiler, the boiler is] tamei. [But if he attached it] on the outer surface [of the boiler, the boiler is] tahor. [If] one patched [the pan] onto the side of [the boiler], whether on the inner surface or the outer surface, it is tahor.