Time-Sert spark plug thread repair kit

I've used many a Time-Serts to repair spark plug threads on small and large cc motors with no failure or issues.
 
#3 spark plug port on my cb550f is stripped and I'm using NGK D7EA for spark plugs. Time-Sert have washer seats available in 9.0, 15.0, 17.5, 22.0mm. Which washer seat length should I use?
 
Back
Top Bottom