These are called cable lugs (also known as cable terminals or lug connectors).
What they look like
What they are used for
1. Connecting cables to equipment
Used to connect thick cables to:
Circuit breakers
Busbars
Batteries
Distribution boards
The hole (ring) is where a bolt passes to fix it tightly.
2. Strong and safe connection
Prevents loose wiring
Ensures good electrical contact
Reduces heat and power loss
3. Used for heavy cables
Common in:
Main power supply
Solar installations
Industrial wiring
Generators
How they are used
Strip the cable insulation
Insert the wire into the lug
Use a crimping tool to press it tight