Hello, hope you are keeeping well. Perhaps someone can assist with this:

I swapped the collimation screws of my Celestron C8 XLT with Bob's Knobs.
They are great as they eliminate need for a wrench, however, I find it awkward
to get the scope collimated. Bob's Knobs came with three distance rings each a 
bit over a millimeter thick. 

Curiously, when I omit the distance rings the scope won't get into focus,
but it does find focus with distance rings. A slight vertical shift of the 
secondary mirror position should not have such an impact. 

Hmmmm, anyway, I lost the original collimation screws wondering where I can 
source them. Any idea and/or collimation advice is most welcome.

Thanks and CheerS
Robert