Tin plated copper is the usual swage for a manual swaging tool - commonly called Nicropress fittings.

Stainless fittings are typically end terminals - fork eyes, etc. They are installed using a roller type swaging tool.

And Tawd is correct - Architectural fittings are not supposed to be load bearing.

One common mistake I see, is people using lifeline fittings for standing rigging. Hey Bob, this fork eye is $5 cheaper than that one, let's use these...