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Accessories - Bob's Knobs Collimation Knobs For Astro-Tech, GSO, IOptron, MallinCam, Orion, TPO 8" F/8 RCT Secondary

Bob's Knobs Collimation Knobs for Astro-Tech, GSO, iOptron, MallinCam, Orion, TPO 8" f/8 RCT Secondary

Bob's Knobs
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Estimated Arrival: Between Oct 07 and Oct 13. *ETA to USA Only

Shipping & Returns: Satisfaction guaranteed 30 day return policy.


We offer knobs for the Astro-Tech, GSO, iOptron Photron, MallinCam VRC, Orion (US), and TPO OS 8”, 10”, 12”, and 16" Ritchey-Crétien secondary. Select knobs for your telescope from the list below. Price is for a complete set of knobs.

Fits: Astro-Tech, GSO, iOptron, MallinCam, Orion (US), and TPO 8" f/8 RCT secondary (solid or truss-tube)


  1. Two sets of knobs, each with a different screw length, are included with your order. Use the length that fits your telescope best. There should be one or two screw thread turns above the secondary housing. In most cases the dust cover will fit without contacting the knobs.
  2. If the dust cover cannot be installed because of knob height, you can use a shower cap in its place.



Black plastic, 16mm (5/8”) diameter


Stainless steel


We know that once you've placed your order, you are anxious to receive it! We make every effort to get your order shipped out to you as quickly as possible.

As soon as you place your order, you will receive an order confirmation e-mail. This means that we have received your order in our system and pre-authorized your credit card for the purchase. We will process the charges to your credit card and your order will ship within five business days from the date of your order. We will send you tracking information within 24 hours of your order leaving the warehouse to the e-mail address you provided when checking out.  If you do not receive tracking information from us within six business days of your order, feel free to follow up with us at

Standard shipping time in the US is between 3-5 business days, though it can vary slightly depending on the destination. We typically For updates on your shipment you can enter your tracking number here.

We distribute nationwide via UPS and Fedex. Unfortunately, at this time we are not able to provide expedited or international shipping.