Magnet distinguishes whether the screw is stainless steel or iron

1.    Magnetic Materials: Regular iron, carbon steel, SUS410, and SUS420 series.

                Iron: Iron is strongly magnetic, and a magnet will be strongly attracted to it.

                  Note: Stainless steel SUS410 and SUS420 series can also exhibit magnetic                                 properties.

2.    Non-magnetic Materials: SUS300 series (SUS302, SUS304, SUS316, etc.).

SUS304: Generally non-magnetic, but it may exhibit weak magnetism (slight attraction) due to impact processing.

SUS316: Completely non-magnetic.