Astromania Adjustable Guiding Scope Ring Set with Plate - 80 mm inside diameter (pair) - for telescope tube diameter or finders 53 to 79mm The guide scope rings from Astromania Optics allow a reliable and above all stable adaption of telescopes parallel to the main instrument. With the knurled thumb screws, the guide scope is adjustable and you can centre a sufficiently bright star in the eyepiece or the the autoguider. And the tube rings are suitable for bigger finder scopes, too. The adaption of the tube rings to the telescope. The Guiding Scope Ring Set has a Vixen style dovetail bar that can be mounted to your telescope in different ways. First, it fits the standard dovetail finder scope base included on many telescopes. Simply slide it into the dovetail base, then tighten the thumbscrew on the base to secure the guide scope in place. The mounting bar has three threaded through-holes: the center hole has ¼"-20 threads and the two larger holes on either side of center have M8 x 1.25 threads. To attach the guide scope bracket to a universal dovetail plate, one way would be to insert a ¼"-20 socket head capscrew of proper length up through the dovetail plate and into the center hole of the bracket?s dovetail bar. Tighten the bolt firmly with an Allen wrench. Then install the universal plate onto your telescope?s tube rings or radius blocks. Alternatively you could attach the bracket using two M8x1.25 screws in the same manner.