Here is what a winding cone looks like without the spring. The threads that grip the inside of the spring coils are ambidextrous, so you can use the same part on either right- or left-hand-wound springs. The cone size is specific for a certain inner diameter of springs, so if you have the wrong size, the cone will slip inside the spring (cone too small), or not fit (cone too big).
Install the stiffening strut on top of the top section of steel doors with the section lying flat. Then install the opener bracket that replaces the center bracket between the top two sections. While you’re working on the sections, protect them from scratches by putting carpet scraps on top of your sawhorses. Now, slide the rollers into the roller brackets.