This is the USB Unifying Receiver dongle you need to use a Logitech K400r wireless keyboard. If you've lost or broken yours or come across a keyboard without one, this is the missing link. YOU WILL RECEIVE THE UNIFYING RECEIVER ONLY. Picture of the keyboard is only for reference to help identify which keyboard it works with. You will not receive a keyboard, just the USB dongle. 

You will need to "pair" the receiver with your particular keyboard. Logitech provides the "Logitech Unifying Software" on its website to perform this one very easy task (see last image).

You download and run the software. It asks you to plug in the USB receiver. It detects that you've done so. Then on the next screen it asks you to turn off your keyboard and turn it back on. It detects this and pairs the device. At that point your keyboard will work with the receiver, and you never have to use the software again.