Anyone know what the difference between AC 41-983 vs 41-993

983's are Double Platinum
993's are Iridium

I have both here. What would you use in a 496 ho

41-983

Yup, if I'm reading this bulletin correctly, the 983's.

http://www.crowleymarine.com/sb/2/13078

NGK's do not touch the gap leave it alone.

If I recall correctly on the app of NGK's TR55IX ----- 7164

BUP, slight derail...kind of.....I'm not sure if you have ever used these, but they are great if you do have to gap a finewire type plug.

Photo is just one companies,,,a few other companies make the same thing. Can be found under search of 'Billet Spark Plug Gapper'

I like that tool but will add --- on double platinum tip spark plugs - (on the tip and the bottom side of the electrode ) you do not touch the gap because you off center the tips that causes misfires. Actually Mercruiser has a video all about that one as well. Thanks for the pics of the tool

How does that tool open up the gap ? I see how easily it can close up a gap but does it have a slot the electrode goes into then turn the knob screw counter clockwise to open up the gap ?

here is what I am talking about in a pic to help understand about gapping the plugs in which can off center the platinum discs, The off center causes misfires. Plus with double platinum tip spark plugs - opening up the gap can ruin the platinum disc on the under side of the electrode depending how or what gap tool is used.

http://shop.advanceautoparts.com/wcs...tinum-plug.jpg