In what set is this brick used?
The specific part (870) is identified in the other answer, however it is part of an assembly with its own part number:

https://www.bricklink.com/v2/catalog/catalogitem.page?P=827#T=C&amp;C=3

827 Vehicle, Tractor Chassis

870's page mentions it has extra parts that it is used with, and 827 is the complete assembly (steering wheel + mechanism).

This page details what other parts are needed to complete it.

https://www.bricklink.com/catalogItemInv.asp?P=827

870 is the base in the picture, and 871-874 are the mechanism pieces.