Keilim 11:3-4

Keilim 11:3

If utensils are made from metal ore, from smelted metal, from the hoop of a wheel, from sheet metal, from metal plate, or from the bases, rims or handles of wooden utensils, or from metal shavings or filings, they do not require purification before use. Rabbi Yochanan ben Nuri says the same is true for utensils made of the cut-off pieces of utensils. If they were made from the pieces of broken utensils, from scrap metal or from nails that are known to have been made from utensils, they are ritually unclean. If they were made from nails of unknown origin, Beis Shammai say they’re unclean and Beis Hillel say they’re clean.

Keilim 11:4

If ritually unclean iron was smelted together with ritually clean iron, if most came from the unclean, a utensil made of the resulting metal is unclean; if most came from the clean, such a utensil is clean. If the two metals were equal, a utensil made of the resulting metal is unclean. The same is true of a mixture of cement and dung. A detachable door bolt is susceptible to ritual impurity but one that is only metal-plated is insusceptible. The pins and cylinder of a lock are susceptible to impurity. Rabbi Yehoshua says that one may remove the aforementioned door bolt from one door and hang it on another on Shabbos; Rabbi Tarfon says that it may be carried around in a courtyard just like any other utensil.