A few months ago, a friend wrote to ask...
"Is there a difference between 316 and 18-8 stainless steel springs in bolt snaps? The 316 one is $6 and the 18-8 is $14. Is there that much of a quality difference in the different alloy? Thanks!"
My response:
I have to admit that at first I thought the 316 ones were more expensive and not less!
18-8 SS is identical to 304 SS, I believe.
316 is much more corrosion resistant, particularly to the chlorides in salt water. Which makes a longer-lasting spring is an entirely different question. I am not an engineer, but I found a site that talks about fatigue resistance. It says 316 is somewhat better than 304 here, which I would expect to mean that springs made from it would last longer. Here's that site:
Article: Fatigue properties and endurance limits of stainless steels
Most metals including SS are priced per pound. While 304 and 316 are not that far apart in cost, 304 is actually less expensive (316 runs about 25% more than 304). Here's a site that sells metals:
Buymetal.com - Online Metal Store
316 machines much more easily and has a lower melting point (for casting things like bolt snaps) than 304, so it's probably cheaper to make bolt snaps from 316. This might be why the ones made from 304 cost more, or it could just be their choice of supplier.
The net is that I'd probably go for 316, and even more so if it's cheaper than 304.
(That said, I'm a cheap so-and-so and I just use brass ones.)