Standard Fitting 1.25" Telescope 3x Barlow for Increasing Your Magnification Three Times By Dragonfly Optical 3x Barlow lens that Triples 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