Medic1210,
I have a couple of those snap clips. Got them at a boat/marine shop. PM me and I can give you the names of a couple of on line places that sell them. They are a very good design. The gate is a very clever use of a torsion bar, which minimizes the metal fatigue, so they last a looooooooong time. That is one of the design factors that attracted me to them. I've seen other types of snap clips fail when one of the spring components fail from fatigue.
The S biners use a similar gate set up, but they don't look as robust.
The one I have on my key ring is over 30 years old and still very useable. Mine doesn't have a stamp indicating what type os SS it is made from. I think it's 316L.
I have some of the small ones that have been in use for several years without any problems.
Ric