Hello,
I have never replied to one of these before so I hope it works, any way the Cobra Flex II horn is a a 1 3/8 threaded horn and it does work very well. I have only seen it used with University sound drivers though.
When I worked for Altec/University sound I did a lot of testing with that horn and drivers. The problem is all the US drivers only played out to about 5 to 6 Khz so I can tell you they work well as a midrange horn they have a very smooth response using drivers like the ID40 and ID60. The ID30 works pretty good but I would go either of the first two.
I may have some old spec sheets at work if you wanted to call me at 405-789-0221.Best Regards,
Bill Hanuschak
Great Plains Audio