How to tell if screws are stainless steel or not?

not 100% accurate, as it depends on the composition, but ss is generally non-magnetic!!

Jon

Stainless steel fixings are commonly made from an austenitic stainless steel, which is non-magnetic.

Colin Bignell

Why do spoons stick to magnets?

Unfortunately some ss sticks to magnets and some doesn't. I haven't got a clue which type of ss screws are made of.

A plated brass screw won't attract a magnet but could look like a ss one.

sponix

Stick it in a glass of salt water and see if it rusts :-)

But, AIUI, the screw forming operation, which involves large amounts of cold working, can make it magnetic, even if it normally wouldn't be.

Austinitic stainless steel is non-magnetic. Martensitic and, to a lesser degree, ferritic stainless steels are magnetic. Fastenings are usually made from austentic stainless steel. Spons are more often from a martensitic stainless steel.

Breathe on it. If the haze looks bluish, it is chrome plate. Otherwise, it is not.

Colin Bignell

Zinc and brass taste bitter but stainless steel tastes sweet. So lick them and find out.

The most common alloy for fastenings, 302 stainless steel, remains non-magnetic, even after extensive cold working. Other alloys can have greater changes in their magnetic permeability after cold working, but the difference from a carbon steel fastening will still be quite obvious.

Colin Bignell

try the spak test on a grinding wheel. Different metals give different sparks (needs research as it is a long time since my apprenticeship)