More about the series Series 4000...
A compact "shorty" type 1.25" Barlow
Doubles the magnification of your 1.25" eyepiece while offering excellent image quality. Features a 26mm lens aperture, 1.25" barrel, multi-coated optics, and doubles the power of any 1.25" eyepiece without adding a very long extension between the telescope and the eyepiece. Insert this into the telescope's eyepiece holder first, and then insert your eyepiece into the Barlow.
May also be used in a diagonal mirror either between the diagonal and eyepiece for a 2x magnification factor or between the eyepiece holder and diagonal for a magnification of approximately 3x. Compatible with nearly any telescope which uses 1.25" eyepieces regardless of brand and even those with limited focus range.