If you have selected a torsion spring option, and are installing the door yourself (DIY), then you will need to wind the springs during the install to set the tension. The Winding Bars are tools to manually wind the torsion springs. The Winding Device is a tool that attaches to a drill to set the tension of the torsion spring. If you are installing a door with tensions springs on your own (DIY) we recommend purchasing the winding device as it will make the install much easier. If you are having your door professionally installed, you do not need to bother purchasing either device.