Reference for Chullin 245:37

כמה כדי אחיזה טפח כפול

for since he did not shrink from immersing it, he likewise will not shrink from tearing the greater part of it; but it does not apply to a garment which had not been immersed that same day, for it is to be feared that he will not tear the greater part of it.

Jastrow

Jastrow

Jastrow