Nothing to worry about - just chalk that up to conversion or convention practices.

That small of a difference is pretty much a wash, in terms of performance to a plug.

The one thousandths of a inch difference is likely this is from rounding error when you convert from metric to SAE numbers (plug gap is 1.1mm or 0.0433") or even buried from old school SAE measurement tools, as back then - the vernier calipers and screw micrometers couldn't resolve past 0.001 inch repeatedly, i.e, the rule markings couldn't get that close - too wide to measure this distance.

Should be pre-gapped at 0.043" or 0.044" - depends on the series of plug, when they were made, what batch.

I've seen pregapped plugs run perfectly spot on to as badly as 0.010" off ! That's why I always double check the gap.

What happens if the gap is off and you don't check before you install them? Likely nothing will happen, as long as your engine was running well before.

Granted that some engines are more sensitive than others, most engines can tolerate a significant amount of variance in the plugs - only when the plugs have sufficiently started to wear down will you see that variance start to come into play. Some like to start off with plugs slightly closed in gap, some like it slightly wider.

Make sure you use a wire-type sparkplug feeler gauge. Regular "flat" feeler gauges can crack the electrodes on the plugs, if you are not careful.

That one is fine - lots of different designs of those feeler gauges - as long as it is a wire type, you are good to go. That particular one is useful for multi-prong plugs, but will work for standard plugs just fine.

Pretty sure we talked about this before at length - just check your earlier posts on that. Mine is also a wire-type gauge.

As for checking plugs, generally safest to use a wire-type gauge on ANY plug. More critical on iridium and platinum plugs, as the electrodes are harder and more brittle - greater chance to chip the electrode trying jam a conventional flat gauge or one of the ramp type gauges.

? This a question or are you making a statement ?

Threads are 14mm diameter, 19mm reach

Size of socket you need is 5/8" or 16mm

Flat? You mean it has a gasket vs taper?

Flat? You mean has a gasket? I think that is the case, they have gaskets on the plugs.

All of this information is on the Denso website. You'll also find out immediately, once you see the plugs in person. Only thing you really need are a 10mm socket to remove the bolt holding the plug on coil ignitors and a decent extension with a 5/8" spark plug socket to get at the plugs.

Read the instructions on the sparkplug package to figure out how much to tighten them back up once you replace them - change the plugs one at a time - note how the plugs look when they come out and which plug came out of what cylinder for future diagnostics.

If all the plugs "read" the same / show the same amount of wear and deposits - you have nothing to worry about - means the car is running well.

Check the flap/tab on the box, instructions are sometimes printed on the tabs - only visible when the box is opened.

If they don't list torque or similar ratings, then just turn it another 1/2 to 2/3 of a turn, after the plug touches the bottom of the seat. This is usually typical for flat seat, crush washer equipped plugs.