I bought this few weeks back, in order to add off axis guiding to my 12" sct on G11 simply to avoid guide scopes. There are many other companies which sale off axis guider but due to finish I preferred starlight express! This produce finish is really very good. There is no doubt about that. But my over all experience in buying this off axis guider and other small things needed like this 12mm ring has been little irritating! first of all starlight express website or OPT do not show the image of the exact product that is offered. e.g. this 12mm OAG extension ring shows 4 items. 1. off axis guider, 2. extension ring , 3. a female thread ( on the right side of this OAG ) 4. male thread ( T) which goes into your CCD camera. Same image is displayed for the OAG also. First when I ordered OAG i was stunned to see that there was no way to connect it to the standard threads. Then I realized after going through SX ccd webside that probably I need to order this connector rings separably. So I ordered them. Then I realized that I could put only one ring on OAG! Thing is you can use this OAG only with SX filter wheel, or extension tubes that SX provides. I could not find it written clearly anywhere. So finally I got this extension ring. I really like the finish as I said. But all these 4 things are put together with 0 size screws which are not supplied with this. These screws are annoyingly small and I jammed 2 of them in to one of the connector ring. I later have to put a notch in these screws to thread them out that put lot of scars on otherwise good looking ring. So in all a nice looking product but very tedious to put it to work.