This is a simple holder that allows you to have a small breadboard just on top of your Uno. It uses the original screw hole of the Uno.Designed for small breadboards with 17x2 blocks (35x50mm), these are usually provided with double-sided tape on their backside, so just glue them in place.It leaves full access to all IO pins on the long sides of the Uno as well as the reset button.It seems that the STL file is upside-down so double-check in your slicer before printing !