MX240 5RU & 2x MPCs

https://www.juniper.net/documentation/en_US/release-independent/junos/information-products/pathway-pages/mx-series/mx240/index.html

The MX240 router is five rack units (U) tall. 

https://www.oreilly.com/library/view/juniper-mx-series/9781491932711/ch01.html

The Routing Engine is installed into an SCB and will be described in more detail later in the chapter.