Standard Fitting 1.25" Telescope 2x Barlow for DOUBLING Your Magnification By Dragonfly Optical 2x Barlow lens that doubles the magnification Tube fitting Size: 1.25 in (31.75 mm) Barlow lenses mount into either your telescope's focuser or visual back. 1st choice among amateur astronomers who want the best performance from their optics. Amazingly compact and lightweight