Steel is definitely the preferred choice here. A stainless screw in a
steel hole will tend to corrode the steel aggressively. Probably worse
in an iron hole. If stainless is all you can find, smear some Vaseline
in the hole and on the screw to seal out moisture and limit the
corrosion. And just in case anyone is confused, we're not talking about
a 3 point slot in the head like some security screws. Tri-lobed screws
have the threaded shaft section gently squished on three sides so the
end looks a little like the rotor of a Wankel engine. I mis-typed, they
are not self tapping screws, technically thread forming screws. Search
on Taptite or shakeproof screws for more info.
Chris
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