Gen II Spark Plugs - OE Denso SK16R11 (3324) vs Denso SK16RP11 (3353)

With 125,000 miles on my 2004 Prius I'm thinking of replacing my spark plugs.

I was thinking I might be lazy and let my local dealer, Sunnyvale Toyota, install them, then I did some research here in Priuschat. The process of installing the plugs sounds straightforward enough (as long as the old ones aren't "frozen" in place). Looks like I should be able to change them out in an hour or less. OE replacement Denso plugs are around ten bucks each on Amazon and RockAuto. And Sunnyvale Toyota charges $234 for this service. I could stand to save most of that money.

Now that I've decided to change the plugs myself, I'm looking to order them online.
I see that Denso makes the OE part SK16R11 (3324), plus a slightly more expensive variant SK16RP11 (3353) they also show as appropriate for the Prius.

What I haven't been able to figure out is the difference between these two Denso plugs.
Their specs on the Denso site look identical. Both have a platinum ground strap.

Does anybody know what the difference is?

Thanks.

 

I wrote to Denso via their website Contact Us: DENSO Iridium and asked about the difference between the SK16R11 and the SK16RP11 plugs.
After ten days I did not get a response, so I called their customer service at (310) 834-6352 and just spoke with Deanna.

She explained that the heat range is the same, the P means there is a double layer of Platinum - 1.55 mm projected.

I still am not sure what benefit this brings for my Prius, but at least I have more information.

It's only a buck or two per plug more for the RP variant, so that's what I'll probably go with.

/Gordon

 

And now that I've talked with them, I found the page on the Denso web site that decodes their spark plug numbers.

DENSO SPARK PLUGS