Orion 13031 Basic 1.25-Inch Rack-and-Pinion Telescope Focuser Precision 1.25" focuser with a smooth adjusting rack-and-pinion design is ideal upgrade for a low-quality focuser or for home-built telescope projects Universal fit base made of durable plastic to fit Newtonian reflector telescopes of 4" aperture and larger Focuser accepts 1.25" telescope eyepieces Has 1-15/16" of focus travel with a fully racked-in height of 3-1/4" Dual knurled focus knobs turn smoothly even with gloves on