Correct, except it's actually a 10mm bolt. But they might have made a 7400 7-speed Hyperglide Dura Ace hub.
I have a 7400 7-speed Uniglide hub, but that probably wouldn't do you any good. I have the cassette to go with, but once you wear it out, pickings get slim. Especially for the last cog which is threaded to a smaller Dura-Ace-specific size.
you're right. and right to correct me. not good of me leading people astray. thanks.