Extension factor 2x – simply insert a 2 inch eyepiece or a 1.25 inch eyepiece (with the reduction) into the barlow and you have a doubling of the magnification.
Extension factor 1.5x - visually screw the Barlow element into the filter thread of your 2 inch eyepiece or also into the filter thread of the reduction of your 2 inch eyepiece extension and the extension factor is shortened by twice to about 1.5x This increases flexibility.