I'm swapping my plugs out right now, and the ones that I just pulled (Bosch Platinum +2) are quite a bit shorter than the ones I'm replacing them with (Autolite #APP5144)!
Everywhere that I've checked is saying that the 5144 is the correct plug for my '04 4.0 SOHC, but I certainly don't want things smashing into each other!
Thanks
MikeR

 

It sounds like the difference between 1/2" reach plugs vs. 3/4" reach plugs. Someone probably mistakenly installed the 1/2" Bosch plugs in your engine.

 

The Bosch ones are wrong. I installed APP5144 plugs in my truck and nothing has gone wrong. Before I put them in I compared them with the OE ones that I took out, and they were exactly the same.

 

Thanks guys-appreciate the confirmation
MikeR

 

Always stand a plug on it's end. As long as the metal ( the seat to the bottom of the plug is the same it will work. The ceramic insulator only matters where heat dissipation maters. Multi-ground electrode plugs don't give you any advantage vs single electrode. Stick with the Autolite or Motorcraft and keep the OE recommended heat range.