Thanks Rich! It looks like two different combos each have two of either the 21 & 12mm or the 15 &12mm Swirl Killers. Do I need both? Is the 15mm a good one to start with? Also, how about the different kits with the Swirl Killer? Two stage, three stage kits, etc?? Sorry for all the questions as I am definitely a newbie! I appreciate your quick response earlier. I am trying to learn and start right!