Orion 52087 2-Inch Precision Centering Extension Adapter (Black) Handy extension adapter with helical compression mechanism. Precisely centers 2 inch eyepieces and accessories in a 2 inch telescope focuser. Avoid set-screw marks and scratches on your 2" telescope eyepieces and accessories. Ideal for accurate collimation tool use in reflector telescopes. Adds 1.7 inch (43mm) of extension. Handy extension adapter with helical compression mechanism^Precisely centers 2 inch eyepieces and accessories in a 2 inch telescope focuser^Avoid set-screw marks and scratches on your 2" telescope eyepieces and accessories^Ideal for accurate collimation tool use in reflector telescopes^Adds 1.7 inch (43mm) of extension