Keeps your important USB sticks and Bluetooth receivers on-hand.
The cap is carefully designed to prevent the USB device from slipping loose.

It works great with Plugable's Bluetooth and WiFi adapters!
http://plugable.com/products/usb-bt4le
http://plugable.com/products/usb-wifint

Here's a bit more on the design:
http://plugable.com/2015/07/30/adventures-in-stackability-and-modularity