These are massive single pole – double throw (SPDT) sealed relays. This means that when current is applied to the coil it throws a simple changeover switch, terminating the connection from the NC contact to ground and closing the NO contact. Use them to switch high voltage/high current devices.
* SPDT Relay
* Contacts Rated up to 220VAC @ 20A
* Coil Voltage: 5V
* Fully Sealed
* [Datasheet](http://cdn.sparkfun.com/datasheets/Components/General/Relay.JQX-15F.pdf) (JQX-15F/005)
* [Relay Tutorial](http://www.sparkfun.com/tutorials/119)