The Meade SC Thread to 2-inch Accessory Adapter is a two-part adapter tube that lets you use conventional barreled 2-inch prism star diagonals on a Schmidt-Cassegrain's threaded rear cell. Clearance on drive mounted telescopes can cause some issues. With some smaller aperture telescopes and some 2-inch diagonals, the length of this Meade adapter can cause the diagonal to contact the drive base when moving through the forks, or with an Altazimuth mount aimed at the zenith. For this reason, you will need 7.5 inches of space between the rear cell of your SCT and the tallest point of the telescope drive base to allow for minimal clearance. If this isn't possible, by splitting this Meade adapter apart at the threads, the lower portion can be removed and an additional 1.3 inches of clearance can be achieved.