Plugs & coils

[denali]

Just changed plugs on 04rx1m . Machine is new to me. Comp 180,180,175,180.plugs looked ok.except the threaded top part of plug where coil contacts had 2 grooves in all of them? Almost looks like arcing but all 4 had it. Question is don't the plugs have a contact or that treads on top? Do I have the correct plug? Carb cleaning tomorrow should be fun

 

[Mighty]

Sounds like the grooves are from where the contacts grab and hold on.