Bob's Knobs Celestron C8 Metric Collimation Knobs
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Bob's Knobs Celestron C8 Metric Collimation Knobs

  (7 Reviews)
✓ 2 year warranty


2x in stock shipped 1-2 working days

About this product

Model:  bk_c8_met_bo
Part Number:  C8metBO

Bob's Knobs are the BEST option for tool-free collimation.

Simple to fit and easy to use.

Collimate your telescope without an Allen key or screwdriver!

Instructions are supplied but can also be found online as well as useful FAQ.

Images are representative and may not show the exact knob size / threads.

IMPORTANT: Please ensure the Bob's knobs threads and factory screw threads match before installation.

Knobs for C8 f/10 Secondary with Metric Collimation Screw Threads (not for EdgeHD or Hyperstar)

Part: C8metBO (black oxide steel); C8metSS (stainless steel)
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.

Knobs: Black oxide steel (black) or stainless steel (silver), 12 mm (1/2”) diameter
Threads: Black oxide or stainless steel


  1. 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; you may omit the white spacers if your factory screw threads are 10mm long. More information is in our Celestron technical paper.
  2. 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).
  3. Black oxide steel (shown in photos) is for dry environments. Lightly oil the knobs 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.
  4. The factory dust cover will fit normally with Bob's Knobs installed.
  5. 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.

Customer reviews

Average Rating (7 Reviews):  
Write a Review and share your opinions!

Rating (max 5):  
Bobs Knobs ... Necessity
24 November 2022  | 

Ok , I'm a fan of these . Let's get that out of the way first .
Bobs knobs are probably one of the best extras you will buy for your Newtonian or your SCT as they make collimating so easy , especially in an sct . No more fiddling with a screwdriver to centre on those, quite frankly, pathetically small collimation screws. Normally I would say that the cost is a bit high for three screws but this product is a really practical accessory for your scope . There are many "extras" that you can buy in this hobby , Bobs Knobs are a necessity. In my opinion .

Rating (max 5):  
Bobs knobs celestron c8
20 October 2022  | 

Great value, quality made. I would recommend

Rating (max 5):  
Celestron collimation knobs
09 August 2021  | 

Fast delivery, knobs easy to fit and work well!

Rating (max 5):  
Collimation made super easy
12 September 2020  | 

These are a god send and I can collimate my Nexstar in a minute or two. No more screwdrivers dangerously close to the corrector plate. Not much comes as cheap in astronomy and has such a positive impact. Delivered in 2 days

Rating (max 5):  
10 June 2020  | 

Do exactly what they say on the tin, easy to tweak collimation, excellent.

Rating (max 5):  
Collimation is certainly easier.
04 June 2020  | 

The 8" SCT is not a big scope but it's difficult to reach the adjusting screws whilst holding a screwdriver and looking through the eye piece at the same time. Bobs knobs enable me to look through the eye piece and make the adjustments necessary with ease with no risk of damaging anything. It's a cheap mod and well worth the price.

Rating (max 5):  
less risky and super quick way of collimation
29 April 2020  | 

Got an Celestron 8SE and usually spend a substantial amount of time for collimation (I am a newbie on AP ) with my screwdriver in order to not to scratch anything while moving the screws.. It is much much more quicker and less riskier with these knobs. Great product, definitely recommended to all SCT owners.


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