That’s a toggle latch / draw latch - also called a "box latch" or "chest latch"
What it does:
It pulls two surfaces tight together and locks them. You hook the loop over a matching staple/keeper, then flip the lever down. The over-center action keeps it locked tight until you lift it again.
From your pics:
1. Material: Galvanized/zinc plated steel - that silver finish prevents rust
2. Design: One mounting plate with a hole at top for screws/rivets, spring-loaded bail/loop at bottom
3. Size: Looks like 3-4" long - common size for toolboxes, cases, enclosures