Solitude Diver:A lot of the ones you find at the hardware stores are not solid brass or stainless, but are a plated metal (chrome, etc). These tend to corrode and deteriorate faster which can cause them to bind up easier.
However, along those lines, some marine/boat stores sometimes carry solid brass and stainless clips.
Lowe's carries all three,chrome,brass,stainless. I can't say what the internal parts are made of but I would assume stainless as well since mine have held up quite well. I doubt that there is a stainless steel bolt snap manufacturer that makes one stainless steel model for hardware and marine stores and another model for dive stores.