Orion 7381 105mm ID Pair of Guide Scope Rings Two cast-metal rings designed to hold dedicated guide scopes up to 80mm in aperture for guided astrophotography pursuits Each ring features three alignment screws for precise alignment of guide scope with telescope used for astrophotography Interior diameter of each guide scope ring is 105mm - using with guide scopes up to 80mm provides ample alignment adjustment range Non-marring nylon alignment screws will not scratch guide scope finish during alignment adjustments Rings attach to guide scope ring mounting plate (sold separately) with two 1/4"-20 hex-head cap screws (included)