Spark plug wire question

What is the best way to trim the end of the wire after cutting it to the correct length without damaging the conductor wire in the center?

I very carefully sliced through mine with a new razor blade. I bent the lead slightly as I sliced and I was able to cut through the insulation without touching the center.
I don't know if there's a "correct" way but that worked for me...

i run around the insulation with a knife about half way through then twist the insulation off.

A correct set of T-Strippers works well. Small enough to get into tight places and has multiple sizes for different size wire. And nicks in the center conductor are bad. Points off. Applies to general wiring repair too.

What I wound up doing was, I used my regular wire stripper and put the wire in the 12 gauge slot . It cut nicely through the outer casing and then I twisted off it off and it left the center core untouched.