These rings provide the ideal solution. They are made of precision machined aluminium with black anodizing. An Allen key & wrench to adjust position is included. They are also extremely useful when used with a flip mirror or beam splitter for photography. To use a par focal ring with a flip mirror you would first use the telescope's focuser to put your attached camera in perfect focus, now slide a ring over the eyepiece of your choice and raise and lower the eyepiece in the holder until it is perfectly in focus. Once you find the focus point that is perfectly matched to the camera slip the ring down and lock it in place using the included wrench. Now you can focus using the eyepiece . This is much easier than a dim focus screen. You just flip the mirror and take a picture! Leave the ring in place on the eyepiece and you can always quickly and easily pop it back in for photography. The auction is for the 3.2cm version.