Fits Astro-Tech, Orion, GSO and TSO 6? f/9 Ritchey-Chretien OTA’s.Used for attaching telescope OTA to existing mount or attaching accessories to top of OTA. Curved radius blocks and mounting hardware included. Uses existing mounting holes in OTA. 13.5? long, 4.0? wide, .5? thick, Wt. as shown 32 oz.