Well, the G3 & G4 used a different brushroll with the BPI LED on the opposite side of the nozzle to the HeritageII-LII and G5 onwards, they had a more square appearance, where the G5 to Ult. G had a more rounded look, the Sentria going even rounder but still with sharp lines, and the G5 was the first to have the "kevlar" fan (apparently it's not actually Kevlar), the G6 introduced the rounded emtor and HEPA filtration, aswell as the all plastic "crushproof" snap-fit filltube, and of course, they were all different colours, the G5 being the biggest exception being Burgundy red rather than the various shades of Grey the rest came with...
Under the hood they're all pretty much the same, except the Ult.G had an extra speed switch, so it in essence had 4 speeds (Floor-Low, Floor-High, Hose-Low, Hose-High), the Sentria has an LED headlight where the rest had incandescent, the brushrolls with the G3/4 wend from Sleeve bearings to Ball bearings, and changed around the time of the G6 from 4-row to "oblique", and later they altered that brushroll and introduced a new style rugplate to match, the Techgrive gearing between transmission & motor was altered to compensate for skipping on certain carpet types...
And, the bags went from being plain paper to MicronMagic, then from those to MicronMagic HEPA, and then from those to the White MicronMagic HEPA+, and of course they introduces the F-style connection which allows faster fitting of all variants of the Micron Magic bags...
Bored yet?
