Product Description

Details per Individual Knobs Available Below

Knobs for C6 f/10 Secondary with Metric Collimation Screw Threads - Black Oxide Steel (C6BO)

• Fits: Celestron 6” (15 cm) f/10 SCT versions (C6-A-XLT, C6-GT, C6-S, C6-SE, C6-SGT, others)
• Knob: Black oxide steel (black), 12 mm (1/2”) diameter
• Notes:
• 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.

Knobs for C8 f/10 Secondary with Metric Collimation Screw Threads (not for EdgeHD or Hyperstar) - Black Oxide Steel (C8metBO)

• 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.
• Knob: Black oxide steel (black), 12 mm (1/2”) diameter
• 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. Here are some hints to help determine which screws your telescope has. 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 the metric Fastar version only if it does NOT have EdgeHD optics. Scopes with EdgeHD optics require different knobs (Item D below).
• 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.

Knobs for C8 f/10 Secondary with EdgeHD Optics - Black Oxide Steel (C8edgBO)

• Fits: Celestron 8” (20 cm) f/10 SCT with Fastar secondary and EdgeHD optics
• Knob: Black oxide steel (black), 12 mm (1/2”) diameter
• Notes:
• These knobs will fit only the Celestron 8” SCT with Fastar secondary and EdgeHD optics. These telescopes are marked “EDGEHD OPTICS” on the corrector ring. Do not use these knobs on the non-EdgeHD Fastar secondary; the screws on these knobs are too long. Be sure to check that the thread length on our knobs matches the thread length on the factory collimation screws.
• 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 fit normally with Bob’s Knobs installed.

Knobs for C9.25 f/10 Secondary (non-Fastar) with Metric Collimation Screw Threads - Black Oxide Steel (C9.25metBO)

• Fits: Celestron 9.25" (23.5 cm) f/10 SCT versions with metric screw threads (CPC 925). Not for C9.25 with "Trifid" Faster or EdgeHD optics (see Item below).
• Knob: Black oxide steel (black), 12 mm (1/2”) diameter
• Notes:
• Black Phillips factory collimation screws usually have metric threads, but some black Phillips screws have standard threads. Our hints will help you determine which screws are on your telescope. Make sure the knob threads match the factory screw threads before installing the knobs.
• 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.
• These knobs sit inside the tall lip around the perimeter of the secondary, so they may be hard to grasp with two fingers. Adjustments can be made using a thumb or finger against the inside edge of the knob.
• The factory dust cover will fit normally with Bob's Knobs installed.
• If your telescope has a factory-installed plastic cap over the collimation screws, it 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.

Knobs for C9.25 f/10 Secondary with Metric Collimation Screw Threads and “Trifid” Fastar Housing - Black Plastic (C9.25fst)

• Fits: Celestron 9.25” (23.5 cm) f/10 SCT versions with "Trifid" Fastar secondary housing ONLY
• Knob: Black plastic, 15 mm (5/8”) diameter
• Notes:
• These knobs fit only the Celestron 9.25” f/10 SCT with a Fastar secondary which has black Phillips factory collimation screws that are recessed into the secondary housing. These knobs will fit C9.25 Fastar telescopes with or without EdgeHD optics.
• Collimation screws on these telescopes are small with very fine threads. Knobs must be tightened gently (just enough to hold the secondary in place) to prevent damage to either the knob or secondary assembly.
• Knobs include a set of long spacers so they sit slightly above the rotary cover opening. The rotary secondary cover must remain open when the knobs are installed. The cover is cosmetic only and will not affect operation of the telescope.
• The factory dust cover will fit normally with Bob’s Knobs installed.

Knobs for C11 f/10 with Flat Secondary Housing (non-Fastar) and Metric Collimation Screw Threads - Black Oxide Steel (C11metBO)

• Fits: Celestron 11” (28 cm) f/10 SCT versions with flat secondary housing and metric collimation screw threads (most CPC 1100). Does not fit the Starizona Hyperstar secondary (see Item below)
• Knob: Black oxide steel (black), 12 mm (1/2”) diameter
• Notes:
• Black Phillips factory collimation screws usually have metric threads, but some black Phillips screws have standard threads. Our hints will help you determine which screws are on your telescope. Make sure the knob threads match the factory screw threads before installing the knobs.
• 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 fit normally with Bob's Knobs installed.
• If your telescope has a factory-installed plastic cap over the collimation screws, it 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.

Knobs for C11 f/10 with Fastar Secondary Housing and Metric Collimation Screw Threads - Black Plastic (C11metfst)

• Fits: Celestron 11” (28 cm) f/10 SCT versions (metal or carbon fiber tube) with metric thread factory collimation screws and Fastar secondary housing. This housing can have either a "Trifid" rotary cover or a simple knob in the center and no rotary cover. Factory collimation screws are black Phillips. These knobs will fit the C11 with EdgeHD optics. They will also fit the C11 with Starizona Hyperstar only if the collimation screws have metric threads.
• Knob: Black plastic, 16 mm (5/8”) diameter
• Notes:
• These telescopes can have factory collimation screws with either standard or metric threads. Most models with black Phillips collimation screws have metric threads. There are a few black Phillips screws with standard threads. See our hints for more information. If you discover your knobs have the wrong threads, you can return them for a refund and order the correct knobs. Alternatively, you can order knobs with both standard and metric thread screws and return the unused set for a full refund.
• Collimation screws on these telescopes are small with very fine threads. Knobs must be tightened gently (just enough to hold the secondary in place) to prevent damage to either the knob or secondary assembly.
• The factory dust cover will fit normally with Bob’s Knobs installed.
• If your telescope has a rotary secondary cover, it must remain open when the knobs are installed. The cover is cosmetic only and will not affect operation of the telescope.

30mm Knob for Set Screw Secondary - Black Plastic (CNsec30)

• Fits: Celestron C8-N/NGT, C10-N/NGT, Orion Astrograph, Astroview, SkyQuest XX and XT, Skyview, SkyWatcher, StarBlast, GSO, and many others.
• Knob: Black plastic, 13 mm (1/2”) diameter
• Notes:
• Secondary Characteristics: 4-vane spider, a deeply recessed center screw, and factory headless set (grub) collimation screws. The secondary plate holding the screws is about 20 mm (3/4”) thick. This is a very common Newtonian secondary configuration.
• Order knobs with a screw length sufficient to allow the knobs to clear the secondary housing. Knobs with 30 mm screws are the most common in this configuration.