I'm tracing a circuit. What is this part?

[![one side of component](https://i.stack.imgur.com/O1Mji.jpg)](https://i.stack.imgur.com/O1Mji.jpg)

This is back of it.

[![other side of component](https://i.stack.imgur.com/erIZG.jpg)](https://i.stack.imgur.com/erIZG.jpg)