The Vixen Dovetail Tube Plate attaches to the Vixen Great Polaris, Great Polaris DX, GP2, GPD2, Porta, Sphinx, and SXD telescope mounts, as well as the Great Polaris' many 'copies' on the market such as the Celestron CG-5 & Meade LXD75 mounts. This is the plate to choose for most situations where you're just mounting a scope and perhaps a camera atop the scope. If you wish to mount a more complex arrangement of guide scope aside a main scope, or a scope and a large camera setup aside one another, then instead use the #2576 DX Accessory Plate.
The Vixen #2661 dovetail plate's drilled to carry Vixen's tube rings, which hold the telescopes themselves. Atop the tube rings which you would attach to this plate, you can attach Vixen's #3548 Tube Ring Accessory Plate to mount a small camera, finderscope, etc.