Different numbers mean they are made at different ratios of metals. Generally 314 (might be wrong on this one) and 316 (positive on this) are used for fish tanks as they are the most resistant to corrosion.
SS mesh is magnetic so what you can do is just have some small magnets on the outside of your tank. The attraction should work through your tank glass/acrylic and keep the wall on. Most people either just shove the wall far enough down in their substrate or use suction cups.
Grade 304 is economy grade stainless that's plenty safe for a tank. Grade 316 is 50% more expensive, better quality, and perfect for a tank. If you ACTUALLY have one of these of these grades, neither is magnetic (or only slightly)
. Some dirt-bags mislabel plated steel, or crap-grade stainless as 316, but if it's magnetic --> That is the instant tell-tale of fraud.
from wikipedia: http://en.wikipedia.org/wiki/Stainless_steel
"There are different types of stainless steels: when nickel is added, for instance, the austenite structure of iron is stabilized. This crystal structure makes such steels virtually non-magnetic and less brittle at low temperatures."