Inspect at 60,000 miles (96,000 KM)
Replace at 105,000 miles (168,000 KM)
For whatever reason, I replaced mine at 64,000 miles. I had bought it used with 56,000 miles. Now it's at 130,000 miles.
I replaced my spark plugs around 126,000. That was a big boo-boo. The tips were literally worn down.