This is a ring set for mounting 80 mm (3.15-inch) Stellarvue Finderscopes: to the top of a hinged mounting ring. The rings are 96 mm (3.94-inches) ID with stainless steel screws tipped with Nylon, and the base was made to fit two popular ring widths, all in all, a top-notch product in a specific size category.
For the best possible fit, your telescope mounting rings should be either 20 mm or (0.787-inches) thick and have either a 1/4-inch to 20 (6 mm to 20) threaded center hole, which most hinged rings do indeed have. The ring set comes with both a 1/4-inch to 20 and a 6 mm screw. Please, be sure to use the correct one for your ring set.
Drawings included in the Gallery Tab above illustrate the dimensions of most of the components of this item. The base that attaches to the telescope's mounting ring and the standard Stellarvue dovetail rail are both illustrated with their dimensions.