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To avoid counterfeits, check bolts for grade and manufacturer. Photo: Firestone of Lisle (Ill.)

In the last 18 months, non-spec—or counterfeit—parts have again emerged, and fasteners are no exception.

Their offshore manufacturers cut corners or don't adhere to proper specifications. Often made from mild steel, with coatings that fail to protect from corrosion, these substandard parts typically have short life spans.

In the United States, fasteners are made to standards established by the Society of Automotive Engineers, the American Society of Mechanical Engineers, and American Society for Testing and Materials. Lines on the bolt or nut head pointing to the corners of the hex-head identify grades. Three radiating lines point to every other corner for Grade 5, and six point to each corner for Grade 8. Both are tough and able to resist strong lateral forces. A letter or symbol identifies the manufacturer.

Counterfeit bolts are made to lesser standards. Known counterfeits identified by the National Highway Traffic Safety Administration include those marked FM, H, KS, M, MS, NF, RT, or by the lack of a manufacturer's symbol.

The best way to avoid buying counterfeits is to know your source. Beyond that, examine parts against those being replaced.

For instance, substandard parts may weigh less due to weaker materials or thin construction. Often all counterfeit parts in a lot will have the same serial number stamped on them.

But basically, if a deal seems too good to be true, there's a great chance it's counterfeit.