On my 99 ford explorer are the spark plug thread metric or standard?

It could be ignition pack, under the hood, you can verify this by, pulling out one spark plug, Pull the fuse to the fuel pump, clame the threads of the spark plug to the frame of the car. DO NOT TOUCH OR HOLD the spark plug WHILE CRANKING THE CAR. This should not hurt the ECM of the vehicle. If you see a bright blue sparks, its not an ignition issue.
It could also be the spark plug wires. They should be changed approximately at 80K miles.
If there is a check engine light on, take it to a car parts store and they will read the codes, to help troubleshoot the problem.

CYLINDER 3 MISFIRE COULD BE LOOSE SPARK PLUG OR CROSS THREAD SPARK PLUG TO CYLINDER 3 THE CYLINDER COMPRESSION IS BLOWING BY SPARK PLUG MAKING A WHISTLE NOISE.

.0395 = 1mm

1.1 mm x.0395=.043 That is about what a Ford Spark plug is set at.

.052 gap divided x .0395=1.3mm

pretty simple just screw them out and replace them you may need an extention with a swivel but you shouldnt have any major problems, remember to always hand start the plugs in the ports before using a wrench to ensure they are properly threaded.

the spark plugs are located on either side next to the intake manifold you will need to remove the coils to get to them

not press fitted, standard tapered bearings, if 4X4 it is a little more involved, just dont misplace any of the smaller parts and you will be fine.

Any Chilton's or Haynes manual will have it. Did you disconnect the plugs and forget where they go? It is always a good idea (especially in the age of digital cameras) to take some photos of your undo operations to help in the re-do. What engine does your Explorer have?

Use an Allan Wrench

Hi there;
Torque for your spark plugs is 7-15 ft lbs. You want to make sure the engine is not hot when you change them or you may ruin the threads. I also recommend you put some anti-seeze (like zinc-cote or copper cote) on the threads of the plugs to ensure they don't seize in after a long period of time.

Hope this helps
Farrout!

8mm