Why are metal doors, bolts, and locks NOT susceptible to impurity?
Halacha 1: these are not susceptible because they do not have independent vessel names.
Question 2
When a necklace string snaps, what happens to the individual metal links?
Halacha 4: when the string snaps, each link is susceptible independently because each has its own name.
Question 3
When is a metal cover of a receptacle susceptible to impurity?
Halachot 5-6: all metal coverings of receptacles are pure. Exception: when scraped and polished into a mirror — then it has its own name and is susceptible.
Question 4
Broken metal weights — when do they become susceptible again?
Halacha 8: even if broken pieces are brought together and used for weighing, they are not susceptible. Only when properly fixed do they become susceptible.
Question 5
Are the chains of wholesalers susceptible to impurity?
Halacha 12: wholesaler chains are susceptible because they are used to lock the stores — functioning as locks.