Kelim, Chapter Twenty-Nine, Mishnah Three
1) The string of a [common] plumb-line is regarded as connected up to a length of twelve [cubits];
a) That of the carpenters plumb-line, up to eighteen [cubits];
b) And that of the builders plumb-line up to fifty cubits.
c) The parts that exceed these lengths, even if it was desired to retain them, are pure.
2) The plumb-line of plasterers or moulders is regarded as connected whatsoever its length.
Section one: The string of a plumb-line is regarded as connected for most types of plumb-lines as far as is generally necessary to drop the weight. A common plumb-line is only used for twelve cubits, a carpenters’ is used for 18 and a builders for fifty (that’s a pretty high building). Anything beyond that is pure, even if he wishes to retain the extra length.
Section two: Plasterers and moulders work on walls and therefore can use plumb-lines of any length. Therefore, no matter how long it is, it is considered connected.