This pair of precision machined aluminum guide scope rings have a 125mm inner diameter (ID) and are compatible with guide scopes up to 100mm in aperture. The deluxe machined guide scope rings are lightweight at just 4.8 ounces each, yet they're strong enough to not flex during use. Each ring has three knurled aluminum alignment screws positioned equidistantly which allow you to position a guide scope precisely and securely. Thick nylon tips on the alignment screws prevent marking or scratching the guide scope optical tube. The large knurled screws are easily adjusted, even when wearing gloves in cold conditions. Rings include hardware for attachment to the Orion Guide Scope Ring Mounting Bar (sold separately).