Stainless also has a passivated [read higher resistivity] surface.
Poorer RF conductor.

wrote:

Mike:

One thing that no one will tell you is why manufacturers use plated hardware
which rusts instead of stainless. Cost? No. Stainless will not stay tight,
while plated hardware will rust up and then never loosen. So, if you use
stainless, it is highly desirable to use Nylon insert locknuts or else
carefully double nut everything, and add Loctite before assembly. It is no
fun finding another piece of the antenna at the bottom of the tower every
day after the wind blows a while.

--
Crazy George