Bob's Knobs for Celestron 6” SCT The knobs below will fit almost all versions of the Celestron 6” Schmidt-Cassegrain secondary. Price is for a complete set of knobs.IMPORTANT NOTE: Secondary collimation screws have threads (measured below the screw head) that are either 10 mm or 12 mm long. We include a set of white spacers to be used on the knobs if factory threads are 10 mm long. Do NOT use the white spacers if the factory screw threads are 12 mm long.A. Knobs for C6 f/10 Secondary with Metric Collimation Screw ThreadsFits: Celestron 6” (15 cm) f/10 SCT versions (C6-A-XLT, C6-GT, C6-S, C6-SE, C6-SGT, others)Knobs: Black oxide steel (black) , 12 mm (1/2”) diameterThreads: Black oxide All versions of the Celestron C6 SCT have collimation screws with metric threads. Secondary collimation screws have threads (measured below the screw head) that are either 10 mm or 12 mm long. We include a set of white spacers to be used on the knobs if factory threads are 10 mm long. Do NOT use the white spacers if the factory screw threads are 12 mm long. Black oxide steel (shown in photo) 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 usually fit properly with Bob’s Knobs installed, except on some very early versions. In the Box Bob's Knobs for Celestron 6” SCT Black Oxide or Stainless steel
