If you just bored it once or twice over, your stock spark plug will be all you need. A NGK BR10ECM (or corresponding plug from another brand) with a .032" (0.8mm) gap.
Impossible to answer, depends on what model KTM you have.
NGK Spark Plug BR8ECM
bad plug bad plug cap stator
I have a KTM 525 XCW and have to pull the tank (have to pull the seat to pull the tank) to get to the plug. You need a special thin wall plug tool to get down through the head to the spark plug. Good thing they don't foul plugs like a 2 stroke will.
I have a 07 KTM 525 XCW and the manual call for 6mm on plug gap.
br10ecmix
0.60mm
NGK BR8ECM
it means that spark plug is screwed up and you need to cleans or get a new one
We use the nkg br9eix
NGK BR8HS with a .032" (0.8mm) gap
0.7 mm