Articles 

Even in the Best of Worlds Mistakes Happen

2011-02-23

Even the best of designs can be thwarted by some mistake in manufacture. Fasteners are no exception. The fit, form, and function of a fastener and the way it becomes part of an assembled joint can be completely changed by any deviation in its threading, heading, heat treatment, assembly, and even the selection and composition of its basic materials. Several of the most common observed defects in externally threaded fasteners are discussed below. To start with the basics, the material the fastener is made of is more critical to its function than many imagine. As numerous articles published before, here in Fastener World, have attested to; the usage of a particular grade of steel results in a part of a selected range of strength and hardness. Heat-treated, low carbon steel grades produces low tensile, and hardness parts. Higher carbon and alloy steel grades, properly heat-treated, yield parts of significant strength. In answer to the obvious question-why not use high strength parts everywhere? Designs that require some give and take, some spring rate factor in their operation, need bolts that can “flex” and behave in a spring-like manner under load. Low carbon parts fill this requirement. Hard, unyielding joints, and those that need the maximum amount of clamping force are best served by high strength, hardened bolts.