18-inch machined winding bars, 1/2 to 7/16 inch, model 575. The machined profile means the ends are turned to a precise taper rather than just being straight rod, so they fit tighter in the winding cone holes with less wobble. That matters when you're adding turns to a torsion spring because any play in the bar is a safety risk. At 18 inches, you get reasonable leverage for standard residential springs. These are the tool you want if you do spring work regularly and don't want to deal with sloppy-fitting bars. Make sure the 1/2 to 7/16 size matches your cone.