dovetails to mount scopes

[Redbird48oo]

I have an Meade LXD-75 scope mount, I just purchased a larger scope an Orion Pro 8 [8" x 1000 FL]. I need to find a dovetail to be able to mount it on my LXD-75 mount, am so lost, I have no idea what I need to be looking at. Am not even sure as to what length is even best. HELP.... at present I have my astromaster 130 on it, but the dovetail on it is for a socket head cap screw about 5MM maybe 6mm. Rings on 8" scope has a 1/4-20 hex head cap screw...again am so lost on this topic.

[steppenwolf]

You need a Vixen compatible dovetail bar like the medium or large one shown here. Your tube rings attach to the top of the bar.

[Redbird48oo]

okay thank you that helps a lot, but one ? is there a reason for different lengths. I found I can get and 8" or 13" long, why different lengths? is one more suited for larger scope than shorter ones?