Fits: Most Celestron 8” (20 cm) f/10 SCT made in 2005 and later with black Phillips factory collimation screws that have metric threads. Includes SkyWatcher SCT and non-EdgeHD Fastar. Will NOT fit Celestron telescopes made before 2005.Knobs: Black oxide steel (black) or stainless steel (silver), 12 mm (1/2”) diameterThreads: Black oxide or stainless steel. Due to the Canadian weather, we, David Astro, decided to only offer the slightly more expensive, but more durable stainless steel Bob's Knobs.Notes: Most models with black Phillips factory collimation screws require metric knobs. A few post-2005 scopes have black Phillips collimation screws with standard threads. Make sure the knob threads match the factory screw threads before installing the knobs. Some C8 scopes have metric collimation screws that are 10mm long rather than the more common 8mm, and you should install knobs without the white spacers. These knobs will fit themetric Fastar versiononly if it does NOT have EdgeHD optics. Scopes with EdgeHD optics require different knobs. Black oxide steel (shown in photos) is for dry environments. Lightly oil the knob top and knob serrations periodically as an anti-corrosion measure. Stainless steel provides better corrosion protection in coastal or high humidity areas, or in places where dew or other condensation is common. The factory dust cover will fit normally with Bob's Knobs installed. Some telescope versions have a small plastic cover over the factory collimation screws. This cover must be removed and set aside when Bob's Knobs are installed. The cover is cosmetic only and will not affect operation of the scope.
