Without sparks, no petrol engine vehicle would come out of place. That is why spark plugs have been devised. How they work, what requirements they must meet and how they are made ... You can read that below
Gasoline engines are - in contrast to diesel engines - dependent on 'sparks from outside'. Those sparks must come from the spark plugs. Otherwise the gasoline-air mixture will not ignite. The spark plug sparks between the ground and the center electrode. The high voltage that makes the sparks can run in the tens of thousands of Volts and is generated in the ignition coils. The most important thing in that story is that the sparks are exactly on time. If that is not the case, it may result in the engine not running properly or it may even result in engine damage.
Spark plugs deliver top performance in that context. If the engine runs high in revs, they can also do their job up to 60 times per second in classics. They have to do that work at high and low temperatures. Their electrical insulation capacity must be enormous and they must also gas-tightly seal the combustion rooms with operating pressures up to 100 Bar. And those are just a few of the requirements that spark plugs must meet.
In addition, there are also many different types of spark plugs. More than a thousand! The length and diameter differences in the threaded shaft are easy to recognize. The location and number of the ground electrodes and the length of the ceramic insulator can also be seen at a glance.
What remains invisible to us are things like the wall thicknesses of the insulators, the metallic composition of central electrodes and many other things that together determine the deployment possibilities of a certain type of spark plug. The 'heat value' or 'heat degree' is of vital importance in that context.
We have all heard the cry 'heat value'. But what exactly does that mean? That heat value is clearly legible on the spark plug. That is to prevent that a high-revving twelve-cylinder engine with 150 + pk thoughtlessly gets the same spark plugs as a Lada 1200.
This degree of heat indicates how quickly the spark plug in question reaches its optimum working conditions. The working temperature of spark plugs is between the 600-700 degrees Celsius. Spark plugs with a too high heat value quickly become hotter than 850 degrees Celcius. This causes the electrodes to wear quickly, but it is even worse that the heat from the electrodes causes uncontrolled ignition of the mixture.
Spark plugs that are too 'cold', the electrodes do not reach their working temperature. At the then occurring maximum 400 degrees Celsius, the electrodes quickly become dirty with unburnt residues and the dirty spark plugs cause poor engine running or the engine stops.
After the spark plugs have been unscrewed, the spark plugs can be 'read'. The external appearance of the electrodes tells a lot about what is going on inside the cylinders. A reading aid in this matter is below www.beru.com/deutsch/produkte/zuendkerzen/diagnosehilfe.php
The good spark plugs in the right place have to do their work for approximately 60.000 kilometers. But it is advisable to replace them considerably earlier. You don't have to leave it at that for the costs. In addition, old spark plugs increase fuel consumption and may be the reason for the death of your catalytic converter. And catalysts, those are really expensive things!
AMK had the chance to look into the kitchen of spark plug manufacturer Beru. In the French production unit near Lyon, 'eighty' million spark plugs are made every year. And those spark plugs can now be in your classic.
The instruction booklet or workshop manual states which spark plugs should be in your engine. Pay attention to that!
The 'Wonder spark plugs'
Splitfire, Halo, Pulsstar Power Plugs… They all promise more power and less consumption due to a much better and hotter spark. In practice, only the Pulstar spark plugs (no longer available in the Netherlands) with their built-in capacitor have delivered measurable benefits. Three side electrodes or a ring electrode as ground electrode? The spark really only skips at one point. They can't hurt those super spark plugs. And if all goes well, you will receive a nice sticker set… And those platinum iridium copies? These have actually only been developed to allow the spark plugs to run simultaneously with the increasingly longer service intervals. They don't necessarily spark better, they just last longer ...
The production step by step
Spark plugs consist mainly of metal and ceramic material. The insulator is compressed from aluminum oxide beads. The mold is then ground into a model. In this compressed form, the insulators are very susceptible to breakage. That is why the handling of these semi-finished products is done by robots. The stacked insulators then go into the sintering oven to stay there for 30 hours. At a temperature of more than 1.600 degrees, the insulators shrink about twenty% and get their final shape and hardness. After cooling, they are tested for their functioning by means of a voltage test in which the test voltage 20-30 is kiloVolt. After passing this test, the insulators are provided with their texts and they receive a glass for their visible part 
protective layer. The electrode in the spark plug consists of two parts: the ignition pin on which the spark plug cap is mounted and the center electrode. Just like the mass electrodes, these central electrodes are cold pressed from steel. To get rid of their sharp edges, the parts go into a rotary drum with ceramic particles. To improve their service life and their conductivity, the mass and center electrodes are increasingly assigned a copper heart. The electrodes then receive a durable jacket made of nickel alloy. At the wedding between the parts, a conductive glass mass serves as a welding agent that also provides the gas-tight seal between the parts. This phase is done on the conveyor in a continuous oven. The metal body parts of the spark plugs are also cold pressed and have 
staff material as origin. In six fully automatic working steps, a piece of rod material turns into a steel spark plug body. That semi-finished product is then turned to size and is provided with its internal crimping edge in a difficulty. After the ground electrode has been welded on, the thread is rolled up cold and the ground electrode is bent. Beru currently has spark plugs with up to 4 mass electrodes in production. Everything of course in favor of optimum combustion! It is clear that classic spark plugs are generally less exotic. After the lettering in it 
metal, it receives a galvanic treatment in a nickel bath. The nickel layer provides protection against wear and protects the surface. The parts are finally pressed together on the assembly line - with another inner seal. The shrink edge is briefly but vigorously heated and crushed. The shrinkage occurring during the cooling process ensures an absolutely secure connection between the insulator and the metal spark plug body part. After the sealing ring has been pressed into place, the electrode distance is automatically adjusted. Then there is a visual check. Then the spark plugs go on a world tour in their boxes.