SPST simply mean single pole, single throw. The product controls one circuit with one On position. SPDT means that it is a single pole double throw which means it has two ON positions. This can be a variety of circuitry however.

What is a SPDT relay used for?

Relay is a electro-mechanical switch used to control high power application through low power signal electronic circuits, for an example a simple timer circuit working under 5V DC bias can not control high voltage light bulb, by introducing Relay component we can easily control light bulb.

What is the difference between SPDT and DPDT relay?

SPDT vs DPDT The difference between SPDT and DPDT is that SPDT has a single input that connects to two outputs while the DPDT has two SPDT integrated together which enables it to control two circuits together at the same time.