Not hard at all
search Champion spark plug naming system.
or
go to Champion's web page, it is all there.
It is just a little confusing if you don't play with plugs every day of the week
CJ8 is the standard plug
C = short plug
J = 14mm x 3/8" thread with a 13/16 hex
8 = heat range
CJ8Y is the standard plug with a longer electrode
RCJ8 is the standard plug with a higher resistance
RCJ8Y is the standard plug with a higher resistance and a longer electrode.
Then there is a 3 ,4 or 5 digit number on the box.
That is a use number so I can buy them with 3 different gap distances so I don't have to set the gap before fitting.
If I was a car maker and ordered 1,000,000 of them I would get my own number if I wanted them set to a different gap.
Champion make around 4,000 different spark plugs