From Team 449 Wiki
Rivets are a type of fastener used to connect thin (1/8" or less, for the most common kind) pieces. They are fastened in place with a riveter.
Comparison to bolts
Rivets are lighter and smaller than bolts. However, they are not nearly as strong, although enough rivets can usually be fit in place to be strong enough. They are also not removable without a drill, which enlarges the hole too much for it to be used for another rivet of the same size.
The robot chassis is usually riveted. Rivets can be used in pretty much any application where they are not being sheared, as rivets shear easily.