What can you cut with a hack saw?

Hack Saw is the name given to a fine toothed saw intended to cut metal. The blades for these usually have 16 to 24 teeth per inch, but there are progressive pitch blades which have fine teeth at one end and coarser at the other. This makes it easier to start cutting in sheet metal.

Of course, you can cut other hard materials with these fine toothed saws, plastics and so on. The essential point is that the teeth are hardened so as to cut metal. Of course, they will still not cut hardened metal such as a file, or a padlock shank.