Hopefully an easy question: the Bob's Knobs website has 30mm and 35mm screws available for the secondary mirror on a Skywatcher Dobsonian (fits 5-12" scopes) but doesn't specify which ones are best for the 12" dob - it just says to order knobs with sufficient length to clear the secondary housing. As I'm not near my scope (overseas until next month) and hence can't measure it myself, can anyone recommend which length would be best?
I have the SW 12" collapsible. I changed my secondary screws for Bob's Knobs. I too wasn't sure which size either, so I e-mailed them and they recommended 30mm. Bought and fitted them - they work very well, makes collimating much easier.
