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

In times like these it's tempting to take advantage of bargain prices on parts.

I'm not talking about the guy with a van full of parts in plain boxes, sources unknown. I'm referring to when your regular parts supplier offers a “special buy,” in which he's sharing his savings. The supplier may think he's doing you a favor.

But is he?

The 1990 Fastener Act allows distributors to commingle substandard fasteners with good ones, and lots of 50 or fewer are virtually exempt from many quality requirement provisions. So while your supplier may mean well, he also may be inadvertently passing along counterfeit parts.

Fasteners are critical to virtually every vehicle repair. Fastener failures cause accidents, and accidents cause injury and death. You could be held liable.

The best way to avoid buying counterfiets is to know your source (see side-bar). And the best way to avoid fastener failures is to follow proper storage and use procedures.

Nuts And Bolts

The fastener's nut and bolt (or stud or cap screw) hold two or more objects together. Tightening the fastener creates a tension that pulls the head and nut together. They clamp what's between.

When torque is applied to a nut or bolt head, the threads act like wedges pulling on the bolt. The bolt stretches a bit. Elastic forces inside the bolt cause it to spring back to its original shape. The more it's stretched, the stronger the clamping force, but only if elastic limits haven't been reached. Once the limit is reached, permanent deformation destroys the ability to clamp.

The bolt is part of a system that also includes the nut and washers. The nut applies the stretch to the bolt. Washers protect the work and keep the system from backing off and relaxing tension. If any of these are mismatched, the assembly may fail.

To ensure none of the above happens in your garage:

Specify the right size, grade of fastener. Refer to repair manuals to identify fastener grades. For automotive work, use domestic Grade 5 or Grade 8 bolts. You can use Grade 8 in many applications calling for Grade 5, but not in extremely hot areas such as engines, exhaust systems, and brakes.

Never use Grade 5 where Grade 8 is specified, and never mix grades on one work piece or part.

Don't overtighten fasteners. This can stretch them beyond their elastic limits, resulting in permanent deformation and loss of clamping strength. This is especially true with wheel fasteners.

Don't rely on torque-limiting devices. They can transfer too much torque and damage fasteners. When a repair manual calls for a value, use a calibrated torque wrench to achieve the value.

Handle air impact wrenches and torque wrenches carefully. Maintain them according to manufacturers' instructions and recalibrate regularly.

If a wrench is out of adjustment, or if it's applied for just one or two more seconds after starting to slip, it can cause wheel studs to be permanently stretched. This causes the wheel nut to loosen and could lead to a wheel-off incident.

Also, exhaust clamps can be distorted to leak fumes, and manifolds can crack.

Don't overlubricate. If repair manuals call for oil, use just one drop. Too much lubrication makes the clamping force too great.