You'd be a lot more credible if you knew what you were talking about. A lot of good marine hardware is made of 304 grade stainless steel, which is non-magnetic. The cheaper martenistic grades of stainless steel are magnetic, but the 300 series of austenitic stainless steels are not.
You are correct, in general 300 series is not magnetic. However, when it is cold formed (like on a screw machine) it becomes magnetic. So, fasteners will be magnetic. Your answer seems like it came from Wikipedia. If it did you need to be careful. No one verifies if the information is correct.
I am curious what information you are referring to comparing strengths of 304 and 316. The numbers for tensile strength and 0.2% yield strength are:
304 85 ksi tensile and 35 ksi yield
316 85 ksi tensile and 35 ksi yield
And in case you are confusing the low carbon varients:
304L 80 ksi tensile and 30 ksi yield
316L 78 ksi tensile and 30 ksi yield
in this case there is a 2.5% difference in tensile strength which is well within any reasonable safety factor.
I agree with your statement "You would be more credible if you knew what you are talking about".
If you want to verify my numbers they came from the Machinery's Handbook, 25th edition on page 440.