Porcelain
The metal section at the bottom of a spark plug is called the shell. The components of a spark plug are the center electrode, an insulator, a metal shell, and side electrodes.
typical spark plug gap for this engine is 0.035 inch
The insulator keeps the electrode in the center of the plug from contacting the engine block on the outside. if the insulator wasnt there, the plug would have no spark because all the coil energy would go straight to the ground on the circuit, the engine block
One or more spark plug wires could be going bad. The porceline insulator on a spark plug could be cracked.
A spark plug socket has a rubber ring inside to hold the plug inside while it is screwed into position. The rubber ring also keeps the insulator from being damaged during installation.
A is 18 mm, and p is Projected Insulator Type. I'm not sure about pp.
Depends on the year engine. No one gap is correct for all years this engine has been made. Typical spark plug gap is .035 on points type distributor and .044 on an HEI type system.
There is only one conductor in a spark plug wire, it isn't wire though, usually the center is a highly conductive substance like nickel alloy surrounded by silicone insulator. Each spark plug will get it's own wire so a 4 cylinder engine will have 4 spark plug wires.
The spark plug gap for Fiesta 1.4 Zetec is 0.051 inch. This is a typical gap for many of the Ford vehicles.
Temperature difference or "heat range" is that a "hot" spark plug has a long insulator with more surface area exposed in the combustion chamber. This spark plug will stay hotter, helping to burn off residue and deposits. A "cold" spark plug has very little exposure of its ceramic insulator to the combustion chamber. This spark plug will run cooler, however the 25 and 26 are not heat ranges or temperature indicators. You can read more in the related link.
A spark plug is a device that fires the explosive mixture in the typical automotive engine. One can view a chart of the Champion Spark plugs on their official website.
Normally white, possibly a little blackened, but not much