Yeah, we were thinking along the same lines, but there was not even the tiniest amount of magnetic attraction when I tested them. Weird.. Must mean that they are an alloyed steel, but not a normal chromium based like 304/316 (aka. A2/A4 on nuts), or the nuts have been heated to very high temperatur...

Try sticking a magnet on the nuts. Likely they are highly magnetic and quite likely just plain (mild-)steel. Could be 409 'stainless', which will definitely rust and is not suitable for these applications, but as it looks like it's even rusting inside the threads that seems unlikely. Best option wo...

as above, probably plated steel nuts, tho i wonder about exhaust grade stainless which is barely considered stainless. i wonder why they fitted nuts, its cheaper and quicker to just tap it. as above i would remove the nuts completely, plug and tap. Exhaust grade sounds entirely plausible. I find it...

If those are stainless, I’ll eat that handrail. Probably some type of zinc or cadmium plated nut that when welded, burned off the plating. I’d drill them out completely, plug the hole with a new piece of round stock that is pre-tapped for 6mm. You’ll chase your tail and never have the finish you se...

Very belated thanks to all. (This isn't the only forum I've had trouble with getting set up to notify me of new replies...says it is, then...doesn't...)

I've got some custom-manufactured 304 stainless tube posts for a handrail project that were fitted with unknown grade of stainless nuts spaced along the sides, intended to secure stainless wire-rope for more or less the standard cable-handrail look. But the fabricator used the wrong nut size (8mm vs...

Do TIG welds in stainless exhibit hardening or other annoyances for later machining work, such as drilling and tapping? I received some 304 cable-style handrail posts with oversized nuts already welded into them, so I'm wondering if I can weld 'em up and then drill and tap to the correct smaller size.