The Dovetail Plates are the heart of the Losmandy Secondary System. 0.7 inch x 4.0 inches x length of the tube assembly. Dovetail plates may be mounted to the top and bottom of tube assembly for mounting of all D series accessories, making it possible to use both sides of tube for equipment. The dovetail plates, like all accessories in the Losmandy line, are machined for lightness and rigidity from aluminum stock, then black anodized for a tough, corrosion free surface. Celestron dovetail plate for 9.25 inches, bolts to existing holes. Includes curved blocks for precision fit to the tube assembly. Weight: 3.5 lbs. Length: 18.925 inches Hole Separation: 17.25 inches or 16.5 inches Height: top of tube to top of dovetail plate 1.20 inches Thickness: .7 inches There are 2 different versions of the C9.25. Older models have 17.25 inches hole separation. New models have 16.75 inches HS. Please measure the hole separation and advise which option is required at the time of purchase. Part : DC9.25 (17.25 inches)/ DC9.25N (16.5 inches)