If you flip the breadboard over, you will see an adhesive backing allowing you to permanently stick it to the project. If you remove the backing completely, you will see a series of metal strips that are inside the breadboard. These metal strips with clips are responsible for making mechanical and electrical connections to the components you place into the breadboard. When you push a lead into one of the holes, it’s being grabbed by the clips. Some breadboards are made from transparent plastic, so you can see the clips from outside.