This adapter, paired with a 12x1.25mm nut, will allow you to use any 51mm (2 inch) spherical shift knob with a 12x1.25mm thread while maintaining the reverse lockout mechanism of your 2014+ Ford Fiesta ST, Focus ST, or 2015 Mustang.To install, just unscrew your old knob, thread the nut all the way down the lever (you may need to use a washer if the nut is too small to retain the spring), place the adapter on top of the nut, then screw on the new shift knob.