If the car has gone 175K+ miles without the Check Engine Light coming on and giving you a code indicating a misfire, it would seem that you don't have a spark plug thread problem.

Some, but not all of us, have had a spark plug work loose over time (#2 & #3 in my case on a new car) and if not fixed right away, the hot exhaust gases erode the threads that are already misaligned (reason the spark plug came loose). After the erosion occurs, the threads are damaged and need repaired.

Again, if your plugs are still tight, it wouldn't seem to me that you have a spark plug thread problem needing repairs (based on my interpretation of your post).

 

 

That's no big deal IMO. Precious metal plugs wear so slowly, most could outlast the cars they are installed in as long as they don't get fouled out.

Make sure you install your new plugs tight enough.
Too loose can lead to all sorts of problems.

 

I'd like to confirm that your 175K miles on the same plugs also means 175K miles on the same coil packs electronically firing those plugs.

If so, it is a testament to the longevity of the coil packs flawless operation. On the forum, I've seen several owners automatically change out all four (4) coil packs (approx $170 ea at my dealer) as a "wear item" at 100K miles, for example. If they are working, keep using them.

As you noted, the car works fine but I would have changed the plugs out at 100K miles. I have a bunch of motorcycles and each wear out their spark plugs at different rates, so I change the plug with any major service.

 

 

Hey man! I just finished my first spark plug change and valve adjustments on my '13 Fit at 66k miles this morning. There shouldn't be a problem with the threading as long as you are first hand tightening the spark plugs.
Also, a magnetic spark plug socket would be super helpful for this, that cost me a little under $7 at my local autozone.