Here is about 26 inches of #10 ball chain.  I measured the balls to be about 4.5 mm or 0.18 in in diameter.  (Roughly the size of a traditional BB gun bb)  It is stainless steel, so rust and corrosion shouldn’t be a problem.  It also includes a coupling that you could use to make a loop.  It’s the right size to wear around your neck if you wanted.