I have a Bosch 4418 discontinued. They have a 4417. Now, according to the chart at Bosch my original spark plug has a heat range of 8 and the new one has a heat range of 7 slightly cooler.

4418 are hard to find, the price is $15 to $35 EACH. The 4417 is readily available for under 6 bucks each. I bought the last few 4418 at Advance for six bucks but they didn't have enough. Only three.

Let me add I know zero about the engine, I bought it this way and it still runs good. I just thought after 2 years I would replace the plugs with the identical plug.

The Bosch 4108 and 4417, have four electrodes.