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I want to mount a plexiglass logo-plate on my home-office main door, but I had to buy these standoffs.

enter image description here

I bought them on Amazon where the claim was they were stainless steel (inoxidizable).

I have suspect they sent me the worst quality iron. Of course, on Amazon listing these things were particularly shiny, but now these look particularly opaque.

One thing I noticed is that the standoffs smell, and the smell is left on my fingers after I stroke the devices.

Question is: is there a simple homebrew way to tell iron from inox steel?

So far I have tried to search around and found that I might try to induce rust quickly by using HCl and then leave the piece in sea water outdoors. After a week, rust should appear.

I don't have HCl at home at the moment and I want to be sure before getting to buy it.

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    They probably have a protective oil/coating on them. That is what the smell is coming from. Try cleaning them with dish soap and water.
    – crip659
    May 6, 2021 at 12:44
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    I would call them "standoffs" or "studs".
    – isherwood
    May 6, 2021 at 13:23
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    You could polish them up with some buffing compound and a rotary tool, then coat them with something like Polycrylic varnish (or just wax).
    – isherwood
    May 6, 2021 at 13:27
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    Next time, buy them on a reputable site... I cannot stand questions to the general effect of "help me buy cheap junk and have it work out anyway".
    – Harper - Reinstate Monica
    May 6, 2021 at 18:15
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    @HotLicks that is false. 400 series stainless is typically magnetic. More specifically, martensitic and ferritic stainless steels are magnetic.
    – Z4-tier
    May 7, 2021 at 3:01

3 Answers 3

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The term "stainless steel" is a very broad term. There are many types of stainless steel, and on top of that there are more than 150 grades of steel (i.e. each "type" of stainless steel can fall within 150+ "grades" of steel). If you want the gory details check out the wikipedia page on stainless steel.

Personally, when a manufacturer claims they are selling "stainless steel" widgets I view that claim as somewhat deceptive. Sure, the metal really is stainless steel, but when people think of stainless they have something very specific in mind (i.e. it won't rust...but in reality stainless steel rusts all the time).

You can test whether the metal is stainless steel or not by putting it in phosphoric acid or nitric acid. Stainless should not react with either at room temperature. On the other hand, stainless will react with hydrochloric acid...so don't use that.

Here's my recommendation. Do not test with acid. You probably have stainless steel, but it's probably just not a high quality stainless. You already verified that they are not magnetic, which supports the claim that they are made of stainless. The smelly film that is on them is probably an oil/grease of some sort that was added to prevent them from rusting (hence, this is not a high-quality steel).

I have never seen any version of stainless steel rust as fast, or faster, than pure iron or various other iron-based steels. Here is my prediction: if you keeps these things outside you will probably notice some rust within a month or two depending on how wet they get. Within a couple years they may get rusty enough that you will want to replace them...but they will never be as bad as regular old iron. If you want stainless steel that does not rust (it does exist) then you will pay significantly more for it.

If you want to prevent rust just add a thin layer of oil to keep them dry...which is what the manufacturer did already.

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    Depending on the environment and usage, wax or a semi-dry lubricant may be a better option than oil (less likely to wash off or collect dust, more likely to be removed by abrasion).
    – Austin Hemmelgarn
    May 6, 2021 at 21:24
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The fact that they show no trace of rust points to being stainless. If non-magnetic ( or slightly magnetic) would clearly show they are the very common 18-8 austenitic stainless. If magnetic , they could still be ferritic or martensitic stainless . However ,because they are bar stock that makes 18-8 more likely; ferritics are usually flat rolled / sheet products like auto exhaust ( sheet welded into tubing). Smell has nothing to do with any alloy. A magnet is by far the easiest most definitive home test. If magnetic , salt water would show rust overnight on ordinary steels; no rust = stainless. Better, would be a drop of concentrated nitric acid ; a drop will show no affect on any stainless and quickly make a dark spot on ordinary steel.

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Stainless steel is usually not magnetic (strange but true!) so test it with a magnet.

Edit after many helpful comments: Martensitic and ferritic stainless steels are magnetic. However, it is probably not one of these.

Of our stainless eating utensils the better quality forks and spoons are non ferromagnetic. The knife blades of that pattern are strongly attracted to a magnet, but the handles are not. Some of the cheaper flatware is strongly attracted to a magnet. A magnet will not stick to the sides and lids of most of our stainless pots, but snaps hard to the bottoms of those pans which have an iron core. Some stainless pots have an aluminum core for heat flow and the magnet is not attracted to those.

It is probably stainless steel, just low-quality.

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    Not necessarily true! Martensitic and ferritic stainless steels are magnetic.
    – tnknepp
    May 6, 2021 at 12:46
  • @tnknepp agreed. Anyway I still tried and they don't react with the magnet
    – usr-local-ΕΨΗΕΛΩΝ
    May 6, 2021 at 12:47
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    My guess is it is stainless steel, just a low-quality stainless. Just a guess.
    – tnknepp
    May 6, 2021 at 13:14
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    Of our stainless eating utensils the better quality forks and spoons are non ferromagnetic. The knife blades of that pattern are strongly attracted to a magnet, but the handles are not. Some of the cheaper flatware is strongly attracted to a magnet. A magnet will not stick to the sides and lids of most of our stainless pots, but snaps hard to the bottoms of those pans which have an iron core. Some stsinless pots have an aluminum core for hear flow and the magnet is not attracted to those.
    – Jim Stewart
    May 6, 2021 at 15:34
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    This one shouldn't be down voted so much. It needs more detail, but magnetism is one of the first go to tests. You could get a false negative, but on a job site for example, if it's hard to drill, silver metal and won't hold a magnet, it's probably stainless and it might be time to break out the cobalt or carbide or at the very least some cutting oil.
    – K H
    May 8, 2021 at 10:09

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