rear shelf remix

Remix of this:https://makerworld.com/en/models/1306322-10-in-rack-shelves-for-dell-9020-and-lenovo-m720q#profileId-1339707 Made the rear shelf deeper to fit in a LabRax rack. I also created a pin for my setup of 3 M715s stacked together. Used with my deeper rear shelf it fits behind the computers so they can't be pushed backward into the rack.