They're a style of uninsulated crimp connector for joining two or more wires.
310 and 311 are plain copper.
410 and 411 are zinc-plated steel.
https://www.galco.com/techdoc/gb/10-411_cp.pdf

Haha, uh, I'm familiar with what crimp connectors & wire gauge sizes are.
It's the 310.311, 410.411 that I'm curious about & has got me stumped.
I am not an Electrician but my guess is for crimping together ground pigtails in a receptacle or similar box.
