Is there such a thing?

My Merc manual states that an NGK plug is preferred, but I can find a substitute plug by a different manufacturer locally at an auto parts store for a good deal less.  Exactly the same in all respects, as far as I can tell, and the motor seems to be happy with them.

Is there anything I'm missing by using a 'non-preferred' manufacturer, or possibly a 'non-marine' plug?

Yammies also prefer NGK's.  I believe it's a hotter spark IIRC.  You can get them many places including on-line.  They're not any more expensive than quality plugs made by AC or Autolite.

You're buying six plugs at the most.  Is an extra $15 for a set of six that much of a problem?

You're buying six plugs at the most. Is an extra $15 for a set of six that much of a problem?

No, its not that much of a problem, but if all things are equal, I see no reason to spend more than I have to.

If it's just some old junk engine then who cares right?

If it's newer,  why would you put cheap junk plugs in it?  

I would not buy them from a Marine dealer; can get them cheaper else where

I would not buy them from a Marine dealer; can get them cheaper else where

Yes Catt, thanks-  I do get the NGK's from a marine 'store' on eBay for about half of what the local shops charge per plug, and thats what I normally do.  I guess I just wondered if the phrase 'marine grade' really meant anything or not, or if the phrase applied to spark plugs at all.  If not, then would it not be acceptable to just get the same plug in another brand locally, and not have to pay shipping etc and always have them available.

Thats all I was getting at.

Thanks all-

Spark plugs are rated by heat range of the spark given off, you can go up or down in heat range without having much effect on the motor performance. Or you can buy spark plugs ranging from Economical Design, OEM Quality, to Racing Spark Plugs all having different effect on performance.

A lot of auto parts places, especially those situated near boating areas, carry marine parts at a considerably cheaper price than a marine-specific dealer. I'd check out Sears too; my dad's been buying marine batteries from them for years. They might have what you're looking for.

got my ngk at NAPA for about 1/2 of what my local boat shop sells them for.I did have to order them but i always get a set before my old set goes and keep the spares on my boat with the proper socket to put them on.I have run cheaper plugs but for 3 plugs its only a $3.00 savings so I buy NGK .If you trust a cheaper plug then by all means purchase them.I only run mine for 1 year anyway.

I use only use Autolite in my boat and my highly modified BSA chopper.