Ford: whats the diffrent between the spark plug type E,P,PG of ESCORT, spark plug gap, detroit plant

Question
Hi, Ragu
Thank you for your warm heart first.

Before I want to change the spark plugs of my 98 Ford ESCORT,I read the OWNER's GUIDE,
and found
"**replacement double platinum spark plug "EE" will replace "E" and "EG" and "P" will replace "P" and "PG" suffixed plug. Refer to the Engine Data chart for spark plug gap specifications."

I don't know the meaning of it.

so, could you tell me the difference between the type E ,P and PG (EE,EG and P)?
Does it mean that I need to buy different type spark plug for different Cylinder?
Do I need to install them in specific positions?

Thank you again.  

Answer
Marvin you need not to worry .Ford did this for there own benefit when the vehicle came off the assy. line they know what factory did what so this way they know if the cars with ee plugs had a problem it was in mexico's plant.and if  they had a problem with  pg it was in Detroit  plant ect. and then if they ran short on plugs then they would outside purchase them they would have eg ee and so on. now they also had biffrent heat ranges. The only thing you need to know is to replace it with the PP and these will last you 60,000 to 90,000 miles.