USB to SD or other card

First, please excuse me if this is in the wrong place.

I've seen devices that allow you to insert an SD card and use it as a USB thumb drive, but is there a device that does the opposite allowing me to use a usb drive in a card slot? Is this even feasible?

There are no current devices on the market that have those specifications....

REASON: There are so many different size slots that the usb device would be hard to market to fit each one and function properly.

Originally Posted by Spritzer

is there a device that does the opposite allowing me to use a usb drive in a card slot?