The Opticstar 2" Extension Tube will fit in a standard 2" telescope drawtube and will accept 2" eyepieces and other 2" accessories. It is sometimes used to achieve focusing with long focal length eyepieces where focal travel on the telescope is limited. This can sometimes happen with Newtonians and some refractors that have been designed specifically for binoviewer use. This adapter is 78mm (3" approximately) long and will extend the length of the drawtube by 45mm. It has a brass compression ring.