Dovetail bar and radius block set for Vixen VMC260L Cassegrain Telescope. "D" sized dovetail bar lets you mount your telescope tuve on mounts with "D" size saddles. Dovetail bar systems also let you mount a variety of quick mount adapters, guide scope rings and counterweights on your telescope. Optical Tube Assemblies have top and bottom mounting positions for these dovetail bars. Mounting hardware and instructions included.