This is a 0.3X Barlow lens for our ZM series stereo microscopes with 48mm threading. It reduces magnification by 0.7X (0.3X original magnification), and increases the working distance to a maximum of 287mm (11.3in). The mounting thread is 1-7/8" (48mm). Due to the large working-distance, this Barlow lens is only intended for microscopes which support appropriate height-adjustment.