A rivet is like a bolt with a round head and no thread. It's heated white hot and then inserted through two plates. One man (or women called Rosie) held the rivet firm while another hammered the other end with a pneumatic hammer. This forced the hot soft metal to spread and fasten against the hole.
[below: detail of rivets on the Sydney Harbour Bridge]
The rivets have to be as hot as possible so were heated to white-hot state in small furnaces located across the bridge called 'cookers', and then thrown to a catcher who passed them to the riveters.[below: a rivetting team with their cooker from the Brisbane city hall construction] 
Aahh, the days before Health & Safety! Can you imagine what the working conditions were like - hot chunks of metal that could injury and scar you if they hit you, being thrown about, the sparks flying off, while the riveters stood on a steel beam high above the ground??
