This extension works perfectly with the Celestron CGEM mount. I acquired 3 ****** screws and glued cylidrical spacers on each to replace the 3 allen-head bolts that attach the mount head to the top of the extension. This makes set-up and tear-down of the mount much easier. Now I don't have to worry about my refractor striking a tripod leg while slewing. I deducted 1 star for not providing knobs with the extension.
Very good fit and finish, pretty stout and rugged. They forgot to go the extra step and make it easy to use. Be aware that unless you can leave it permanently assembled with the mount head attached all the way to the tripod, you have to disassemble it every time you are finished. Which means you have to assemble it every time you use it. Rather than supplying a longer threaded center screw to attach the extension to the tripod as well as the mount head, you have to take the extension apart to attach it to the base of the mount head. They could also have put a side hole in the extension itself to allow you to get your hand inside to screw the top adapter to the mount head base. Very good fit and finish, but very poor execution of design.