I recently purchased the 30mm Bobs knobs (Stated that it fits for scopes 5"-10" ) for my secondary mirror on the Quattro 250P, the only issue is that its not long enough, am I doing something wrong or do I have to buy the 35mm knobs?
I recently got the 40mm ones from them under this page: http://www.bobsknobs.com/Newt/styled-6/SWMN.html and they work well for me. It looks like you can go up to 45mm for the screw length if that is your preference. If you can find them at 40mm on Amazon that's probably the move.