Shaper sizing is a bit subjective, based roughly on the stroke and overall envelope of the shaper. Most shapers are sized a bit smaller than their actual stroke, as you need overrun on both ends to cut that much. That being said, it may very well be that the 7" and 8" versions of those shapers have the same stroke and the 8" version got an extra inch from the marketing department. Anyone who's worked with both can verify whether that's true or not. This came up with my "10 inch" Lewis, which works out to a max stroke of around 9", making it more of an 8" shaper. Still, they are nice machines to have. Of course I'm a bit shaper crazy, I have 5 shapers and 3 planers. That's after I sold 2 shapers to make some room. Good luck with it.