Originally Posted by HillRider

The HP-7410 is a 1" threaded headset with cartridge bearings and has a stack height of 37.6 mm.

I can't find any reference in Shimano's tech documents to an HP-7700 headset but they do show the 7410. Also, I don't recall Shimano making anything newer than the 7410 version and by the time the 7700-series (9-speed Dura Ace) came out, Shimano was pretty much out of the headset business.