How much can 0.001" gap affect?

One thousandth of an inch you'll never notice. Your feeler gauge may be out that much. Just go by manual spec.

 

You're generally not supposed to try gap iridium plugs or even mechanically measure the gap due to the risk of damaging the coating on the electrode; by the time the plug is replaced the gap will probably be something like 0.050-0.060 anyway.

I just installed NGK Iridium 3764s in my 1MZ with the factory .44 gap and single ground to replace fouled NGK double platinums which were intermittently misfiring; single ground isn't spec but the CEL is gone for the first time in over 100k miles.

 

You're generally not supposed to try gap iridium plugs or even mechanically measure the gap due to the risk of damaging the coating on the electrode; by the time the plug is replaced the gap will probably be something like 0.050-0.060 anyway.

I measured the gaps very gently using clean, smooth, well-cared-for feeler gauges. As for coating, my understanding is that the threads are coated (trivalent metal plating) for anti-seizing properties; I've not come across any literature that says the electrodes are coated.

I had NGK Iridium IX BKR6EIX-11 from 2011, installed unmodified at factory setting of 0.043" gap. After 35k miles, the gap on all four plugs did not change. These plugs were rated for 50k miles. The 35k miles were achieved on a car with wasted spark system (or DIS); so that's equivalent to 70k.

The NGK 3764s you installed in your 1MZ is the exact same one. It is factory set at 0.043" (1.1 mm) gap. Check the "product specifications" on that page. If you enter your Camry info at the top of the page, it will display a "vehicle information" section above the price section telling you to adjust the gap to 0.044".

 

I can check any gap any plug with a gap. So, there are no "you're not supposed to gap"

Bigger gap isn't an issue. I've been known to open up the gap until I get a misfire and then close it. A good strong coil can push a big gap, especially on a naturally aspirated motor. Big gap could lead to more MPG and HP, until you reach the point of misfiring. Small gap is easier to fire on stressed motors(higher compression or boosted).

I would not worry about .001

I can check any gap tool with a micrometer. That is how I know if the wire are accurate. I typically don't recommend wires or the 'quarter-sized' gaping disks. I use a feeler gauge and threaded plug gap tool.

Example of a feeler gauge

Wright Tool 9530 25-Blade Master Feeler Gauge - - Amazon.com

Wright Tool 9530 25-Blade Master Feeler Gauge - - Amazon.com

www.amazon.com

Example of a plug gap tool

https://www.amazon.com/Boost-Monkey-Spark-Threaded-Plugs/dp/B082CXKF28

https://www.amazon.com/dp/B0832PRVNM

The only important thing that I will state is to not break off the platinum, iridium, ruthenium, or unobtainium pads/coatings.

Even though I hate the accuracy of this cheap tool, you insert your plug into hole and open that gap, like opening a can of beer tab.

And, a pull back electrode bending tool hook on a Bosch

Advance Auto Parts - Down for Maintenance

CTA pictures of opening electrode gap here:

https://www.amazon.com/CTA-Tools-3238-Spark-Gauge/dp/B00PISL328