Question: are all spark plug threads the same?
Answer: Threads. There are currently three spark plug thread diameter and pitch sizes used on motorcycles and ATVs: 10 mm x 1.0, 12 mm x 1.25 and 14 mm x 1.25. There are currently two thread reaches (lengths) used: 1/2 inch and 3/4 inch. Never use a spark plug of the wrong reach.