Which of the following is NOT an inspection item that would cause tires to fail?

The correct answer is based on the criteria used during vehicle inspections to determine tire safety and functionality. Nails or other puncture holes that have been properly plugged or patched are generally accepted repair methods, provided they do not compromise the tire's structure or safety performance. Unlike the other options, which directly relate to significant safety risks, such as visible cords or inadequate tread depth, plugged holes are a method to extend the life of a tire if done correctly.

Worn spots showing ply or cord, and regrooving below the original groove depth present immediate safety hazards by exposing the tire's internal structure and reducing traction. Similarly, tires with no tread indicators could indicate insufficient tread depth, impairing performance, particularly in wet or slippery conditions. Thus, while any of these can lead to tire failure, properly repaired nail holes do not inherently cause a tire to fail.