These are mini-wire connectors. They are lightweight and highly insulated for short-circuit protection.  These connectors have 2 cable entries for connecting wires and cables easily. These connectors have a simple screw lock mechanism that holds the wire tightly by tightening a metal screw attached in the middle. These types of connectors are very useful in hot-swapping types of applications. In other words, They are used where the connection may be expected to be removed for servicing or any other purposes. You can also cut them into your desired needs.