Should I gap to my owners manual spec or are they designed to work with the smaller pre-gap they came with?

Harley Davidson recommends 0.40" gap. As to "You should never gap an iridium plug", NGK's website states for Harley Davidson, these should be gapped at 0.40". I've found many websites stating that if re-gap is needed use care not to damage the electrode or the porcelain center. So, it's not that you should not re-gap, it's that you should be extremely careful.

Is this 6r12, if so why does it not say so ?

Because these plugs are IX DCPR7EIX 99 TO 16 HARLEY-DAVIDSON

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NGK Iridium IX DCPR7EIX Spark Plugs for 1999-2016 Harley Davidson Twin Cam (Pair)

Product ID: 334292066

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Details

Brand
NGK
Core Material
Iridium
Thread Size
12mm
Top Material Type
Metal
Vehicle Service Type
Motorcycle

⚡Up to 3HP boost

🔧Pre-gapped for instant install

🛡️Enhanced anti-corrosion shell

Description

⚡ Ignite your Harley’s true potential with NGK Iridium IX!

IRIDIUM EDGE - Ultra-small 25% smaller iridium electrode slashes voltage needs and extends ignition life.
CORROSION SHIELD - New metal shell plating guards against rust, keeping your engine firing flawlessly season after season.
POWER SURGE READY - Unlock up to 3 extra horsepower and feel the difference on every ride.
TAILORED FOR TWINS - Specifically engineered for 1999-2016 Harley Davidson Twin Cam models—ride with confidence.
PRECISION PRE GAPPED - Skip the hassle—these plugs come perfectly pre-set for peak performance out of the box.

NGK Iridium IX DCPR7EIX spark plugs deliver cutting-edge ignition technology with a 25% smaller iridium electrode for reduced voltage demand and longer ignition system life. Pre-gapped for hassle-free installation, these plugs provide up to 3 horsepower gain and feature a new anti-corrosion metal shell plating, optimized specifically for 1999-2016 Harley Davidson Twin Cam motorcycles.

Specifications

Brand	NGK
Core Material	Iridium
Thread Size	12mm
Top Material Type	Metal
Vehicle Service Type	Motorcycle
UPC	700155016542
Manufacturer	NGK
Model	NGK DCPR7EIX
Product Dimensions	8.41 x 2.39 x 2.11 cm; 40.82 g
Item model number	DCPR7EIX
Exterior	Painted
Manufacturer Part Number	DCPR7EIX
Position	Center
Assembly Required	No
Manufacturer	NGK
Country of Origin	USA
Item Weight	40.8 g