The following four conditions may warrant fastener replacement:

1. Elevated temperatures, like welding, could affect heat treatment and/or plating.

Other cautions include:

• Zinc plating starts burning off at 140 degrees F and completely burns off at 250 degrees F.

• Cadmium plating: Completely burns off at 400 degrees F.

• Black finish (thermo-black from heat treat): Exceeding 400 degrees F will destroy heat treatment.

2. Excessive or undue stresses: If one fastener of a group breaks, like one stud out of four on a wheel of a car, it can overstress the remaining fasteners, resulting in their failure.

3. Corrosion: Rust can create stress points that lead to failure and, obviously, if left long enough, can weaken or destroy fasteners.

4. Critical applications: When in doubt, replace these fasteners rather than risk their failure.