The monocle is important to the Steampunk look as the scientific Victorian examines his new experiment.
The monocle is held over one eye by your brow. This version appears to be made of mechanical cogs. It comes on a chain which has a T-bar to fit into a button hole to prevent loss.
Streampunk refers to a sort of steam powered science fiction based on Victorian stories and alternative versions of history. It's fun to dress up and the accessories are just as important as the costumes.