If a person winds a thread from one spool to another, from one rod to another, or from the upper to the lower beam, and similarly the two pieces of a shirt that are sewn together, if a nega appears on one, the other remains ritually clean. If the nega appears on untightened woof threads or stretched warp threads, they are immediately susceptible to nega impurity. Rabbi Shimon says that the warp is only susceptible when the threads are arranged closely together.
If a nega appears on the stretched warp, cloth that was already woven remains ritually clean; if it appears on the woven cloth, the stretched warp remains ritually clean. If a nega appears on a sheet, its protruding fringes must also be burned; if it appears on the fringes, the sheet remains ritually clean. If a nega appears on a shirt, its hem is protected from impurity even if it’s made of purple wool.