When [thread] is rolled from one skein to another, from one spool to another, or from the upper beam to the lower beam, or when two sides of a shirt [that are attached by a single thread] and a nega appears on one side, the second side is tahor. [If a nega appears on the weft thread when it is] inside the shed [lit., in the soul of the loom] or on warp ready [for weaving], they become tamei with negaim immediately. R’ Shimon says: Only if the warp is close together does it become tamei.

[If the nega] appears on the warp that is ready [for weaving], the woven part is tahor. [If] it appears on the woven part, the warp that is ready [for weaving] is tahor. [If] it appears on a sheet, the fringes must be burnt. [If] it appears on the fringes, the sheet is tahor. A nega on a shirt does not make its trim tamei, even if they are red wool.