1972 dart - stopped running while at 50 mph ? no warning

...Have carbon track "punch through" under the contact and down into the female area for the shaft. I already told you to check that maybe you missed it. Examine it carefully or replace.

i saw that , i just was not sure what to look for . but YES , i think there is what you describe " punch through " what is that from ? what causes that ? i replaced it , but want to know the cause , so maybe i can help prevent that from happening again . thanks