Description (From Recipaedia)
A cobblestone block with a wire running across a hole drilled through the middle. This block can conduct electricity when both ends of the embedded wire are a connected to something. This block can be placed with ends pointing north/south, east/west or up/down. It is very useful when there is a need to run electricity through solid walls, or to insulate the wire from unwanted connections with other wires.
Crafting
Uses 6 Cobblestone blocks and 3 wires to craft. You get 3 blocks.
Use
This block is used to transfer electric signals. By using this block, you can make your designs more compact. It will also help hide any wires from the user. When the block is placed, the wire opening will be facing the character.