Mishna Berura Summaries

Siman 12 – Disqualifying the tsitsis

  1. Even if all eight strings snapped, its kasher as long as each remains with the length that is able to make a bow (4cm – 4.8cm).  (ShA1)

Assuming you do not know which string is the end of any of the others:

  1. If only one string snapped off to less than 4cm from the 5th knot, it’s still kasher since you know that the other end is intact. (ShA1)
  1. If a second string snaps off to less than 4cm, it’s possul because it might be the other end of first snapped string. The Ri holds the tsitsis are kasher as long as there remains 4cm to the gedil. Rely on this only when no other tsitsis are available at all, but not for a bracha or for wearing them out to reshus harabim on Shabbos. (ShA1 – MB13)
  1. If a second string snaps, but 4cm remain – it’s kasher. (ShA1)
  1. If any three strings snap to less than 24cm from the first knot, the tsitsis should be changed. Meanwhile you still say a beracha on them and you can wear them out to a reshus harabim on Shabbos. (ShA1 – MB11)
  1. Any time the tsitsis become possul while wearing them, the begged must be removed even if you are standing still. (MB13)