The DVR90 from Losmandy consists of a pair of 3.5" (90mm) guide scope rings designed to attach a guide scope to your telescope kit.
The rings attach to Losmandy "D" style and Vixen "V" style plates via a tool-less dovetail clamp on the bottom of each ring. Once attached, the guide scope may be inserted into the rings and adjusted via three 7075 aluminum positioning screws that feature 1/4" Delrin tips. The I.D. range of these rings is from 2.48" to 3.78".