I just looked this up the other day.
If you want to order some of these plugs at an auto parts store (I use O'Reilley's because that's what's here) you need to give them a different Champion number.
To get the Champion W16Y plug that many feel are good middle of the road plugs, you need to order Champion 561.
O'Reilley's can get you the original Champion 3X for $20 each. It is known as the Champion 429.
If you want a Champion W18, you order a Champion 518.
Hope this helps.