Hi Chris,
Definitely check it with a magnet.
Here's the link to
Pot Metal from Wikipedia. Basically it's an alloy of various metals which have a low melting point (cheaper to melt at lower temp, and not much strenght) which allows manufacturers to make an
inexpensive casting of an object. It usually has little, if any, iron in the mix as that would raise the melting point, which requires more energy to melt, and thus more expensive to produce. The driving force behind pot metal is CHEAP! :)
In the link above, an important line is this: "Depending on the exact metals "thrown into the pot," pot metal can become unstable over time, as it has a tendency to bend, distort, crack, shatter, and pit with age. The low boiling point of zinc and fast cooling of newly cast parts often trap air bubbles within the cast part, weakening it." So this kind of makes it a "ticking time-bomb", so to speak.
The replacement parts, and I assume the new Tri-Mark locks, use steel for the part which provides considerably more strength and is more ductile and less brittle, so it's very unlikely to crack. And steel, with its high iron content, is magnetic. Hence why a magnet test will easily show which type of metal yours if made from.
Hope this helps.
~Rick
