What is the difference between the two? I just bought some Ngk plugs for my FD, but I went online to try to get a better price on them and noticed those tags. Sorry if this is a newb question, i just am interested to know so I dont get the wrong plugs, or so I can replace the ones I bought.

Also, if anyone has an online store they know of where you can get Ngk plugs for less than 9 bucks a pop please post.

Thanks

 

Without starting a technical lecture
(you can google/search on your own), they identify where the plugs go in the engine. There is an upper and lower spark plug for each rotor. Best way to remember:
Top = Trailing
Lower = Leading

 

Basically the stock trailing plugs are a colder range. 9s instead of 7s.
Since they are covered/blocked they do not cool off as well as the leading.

You would have to see a good picture of the rotor housing to see what I am talking about.

 

Thank you