It's ok, i'm still kinda one myself...anyways, the number of inside gears and strength, hence the names. Go to UE and you'll see. the 6 use the plastic cups, the 8's use the aluminum. Trust me, you want the eights for the money.....here is a link 6's
http://www.unlimitedengineering.com/...ore/13542.html
8's
http://www.unlimitedengineering.com/...ore/13543.html