Celestron 8 inch (20 cm) f/10 Post-1980 SCT with factory Allen, silver Phillips, or headless set-style 6-32 collimation screws, with or without Fastar compatible secondary (C8 black, or gray; Ultima 2000; NexStar 8, others). Will not fit pre-1980 orange tube or most scopes with black Phillips factory collimation screws.
Note1: These knobs will fit C8 models made prior to 2005, and post-2005 models with silver factory collimation screws.
Note2: Most models with black Phillips factory collimation screws require C8 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.
Note3: 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.
Note4: We provide spacers for knobs installed on the Fastar compatible secondary to raise the knobs slightly for easier use. These spacers can be optionally used on other models with Allen or Phillips factory collimation screws to raise the knobs for easier access, but check that the full-aperture dust cover fits without contacting the knobs. Spacers should not be used on telescopes with headless set-style factory collimation screws such as those found on the earlier orange-tube models.
Note5: These knobs will not fit pre-1980 orange tube C8 SCTs.