(This question arises in examining ferrography results of lube oil.)

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If the SS is an Austenitic variety small wear particles are usually magnetic.  How magnetic depends on the amount of cold work involved.   Another property of very fine SS wear particles is that they will sometimes rust.
If you want to be sure and don't have any analytical facilities you can put a drop of 50/50v HNO3 on the particles if there is a reaction it is not stainless.  Another way is to heat the particles a little beyond dark red with a torch and let cool, if they lose their magnetic properties it is probably stainless.   

you can also collect your particles and pass a magnet over them.

damienk - The implication of the question is that this has already been done - the particles are ferro-magetic and electricpete is trying to identify the source.