Electrode configurations - Fine-wire center electrodes provide better sparking and enhanced ignitability. Fine-wire ground electrodes further improve the ignitability of the plug. I read somewhere that the 7500 mile recommendation was mostly to avoid serious carbon buildup on the threads being a small portion of the shell protrudes into the combustion chamber. If carbon is allowed to accumulate too heavily then when you finally do remove them it can damage the head on the way out. Also note that the voltage required to jump the gap increases quite dramatically when the center electrode loses its' sharp edge which then puts more of a demand on the coils and secondary ignition system. I like the Iridium plugs because of their fine wire electrode which maintains the voltage to fire similar to new for many more miles. NGK is the brand leader in the UK spark plug market and are the world's biggest supplier to many major car manufacturers. Each and every one of their products are designed to meet the most rigorous standards and are the professionals' choice because of their quality and technical excellence. Their plugs can be found in use by teams in F1, WRC and MotoGP. Put simply, NGK genuine spark plugs are the workhorse at the heart of smooth-running engines around the world. I changed the factory original plugs on my bike at 15,000 miles. The plug gaps were all still within the 0.8 - 0.9mm spec. There was a little wear on the electrodes (mostly the centre electrode which had lost its sharp edge) but nothing serious, no significant erosion of the electrodes, the plugs were still perfectly usable with no carbon build-up at all. There was no difference to performance when the new plugs were fitted. Those plugs can easily run to 20,000 miles.

Electrode materials - Many use precious metals such as platinum or gold/palladium for greater durability and lower voltage requirements. NGK is the brand leader in the UK spark plug market and are the world's biggest supplier to many major motorcycle manufacturers. The NGK Standard Spark Plug is constructed from durable material that is corrosion and abrasion resistant. The spark plug insulators are made of 99 percent pure alumina silicate, allowing for longer insulator noses for reduced fouling. This spark plug features a triple gasket sealing process that eliminates fuel leakage. It also includes a solid copper core that provides superior heat dissipation and conductivity. This spark plug has resistor that is produced with a glass and carbon mixture, which is fired to ensure superior performance and durability. It has corrugated ribs that prevent flashover and cold rolled threads to inhibit damage to the cylinder head. I've posted on this subject previously: based on experience with my own 2017 Gen 3 SV650, changing the plugs at 7,500 miles is bullshit. The owner's manual that came with my bike has two separate service schedules printed in it: one for 'Europe & Oceania', one for 'rest of the World' (i.e. the USA etc). Insulator configurations - Special configurations are used for the insulator noses to improve throttle response.The NGK Standard Spark Plug is constructed from durable material that is corrosion and abrasion resistant. The spark plug insulators are made of 99 percent pure alumina silicate, allowing for longer insulator noses for reduced fouling. This spark plug features a triple gasket sealing process that eliminates fuel leakage. It also includes a solid copper core that provides superior heat dissipation and conductivity. The spark plug's resistor is manufactured from a mixture of glass and carbon, which is fired to ensure superior performance and durability. It has corrugated ribs that prevent flashover and cold rolled threads to inhibit damage to the cylinder head.