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.

slightly cooler ain't gonna kill you. Wallace racing has good plug reading pics. Just me I would get a std 1 electrode plug & alot of them nowadays are overseas questionable quality. iirc NGK & autolite (from threads here) are reasonably good quality.