Bob's Knobs for Astro-Tech AT6RC Secondary: Streamlined Telescope Adjustment Designed for Multiple Telescope Brands: Suitable for Astro-Tech, GSO, iOptron, MallinCam, Orion (US), and TPO 6" f/9 Ritchey-Crétien (RCT) secondary mirrors, compatible with both solid and truss-tube designs. Product Details - Part: AT6RC: Compatibility: Specifically tailored for the secondary of 6" f/9 RCT telescopes from a range of manufacturers. Knob Specifications: Made from black plastic, each knob has a diameter of 16 mm (5/8”) for easy handling and accurate adjustments. Thread Quality: Constructed with robust stainless steel threads for enhanced durability and reliability. Practical Usage Notes: Dust Cover Solution: If the original dust cover doesn’t fit due to the knob height, a shower cap can be used as an effective alternative. Simple and Efficient Installation: Designed for effortless installation, offering a convenient solution for secondary mirror adjustments. Optimize Your Telescope’s Performance: A must-have for astronomers looking to easily fine-tune their telescope for precise observations.