Persons of a certain age or experience will immediately recognize the shape of this object as describing its purpose:
It is a 5¼” (5.25 inch) floppy disk drive shipping insert to keep the drive heads from bouncing and striking too much. The label on the bottom right, that would stick out at the end user, is particularly amusing:
As an aside, I once pickt up an Apple IIe with floppy drives that once belonged to the Philadelphia School District. How do I know? because they BURNED THEIR NAME INTO THE SIDE OF IT WITH A BRANDING IRON. Hard core.