Rear gear spacers?

I was browsing on summit yesterday, and theres this spacers for rear gears, idk what they do.

Would that spacer allow me to use a series 3 gear in my series 2? or are they made for something completely different...

link: http://store.summitracing.com/egnsearch.asp?N=700+4294925134+4294839047+115+4294 875281

These allow for the use of say 4.10 ring and pinion on a carrier that was only designed for gears, say up to 3.73 or so.