For the Celestron 6SE, you will need to measure the outside diameter of the flange of the stock focuser (the part of the stock focuser that mates to the rear cell, as Celestron uses 2 different size of flanges, 1 that is 1.5"/38mm and 1 that is 1.6"/40.6mm. Starlight Instruments has both of the size of flanges, so please let us know which size flange you have so we can send you the correct one.
Feather Touch® Micro Telescope Focuser for Celestron CPC-800 / NexStar 6SE & 8SE Schmidt-Cassegrain Telescopes
If your telescope is less than a few years old, check the style of the back cell to see which version of the Feather Touch® SCT Micro Focuser you need: If your telescope has a flat back (left picture), you need the standard "C" Micro Focuser. If your telescope has a triangular pattern on the back (right picture), you will need the "CPC" version of the Micro Focuser.
When manually focusing your CCD or DSLR camera for Astrophotography isn't enough, add Starlight Instruments’ "Focuser Boss Digital Kit" for improved accuracy and ease allows automated focusing using FocusMax or any of the many automated focusing software.