Solomark 1.25 Inch to 0.965 Inch Telescope Eyepiece Adapter Telescope adaptation - 1.25" male barrel Eyepiece adaptation - 24.5mm (0.965") inside Filterthread for 1.25" filters Many old eyepieces, including some with a very good optical quality (e.g. Zeiss), have the old 24.5mm barrel diameter (0.965"). If you want to use these eyepieces on a telescope with 1.25" focuser you need this adaptor.