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Selecting The Proper Fastener

At their core, fasteners are simple. They hold everything together. But choosing the right fastener requires understanding some fairly confusing terms. Here are our Top Five.

Tension Strength: The point at which a fastener fails under a load exerted in two direct and opposite directions. Fastener tension is created when a fastener elongates during tightening, producing the clamp load that prevents movement between joint members. Such movement is arguably the most common cause of structural joint failures. See figure A.

Torsion Strength: With Torsion testing, we are able to simulate real life service conditions, check product quality, and ensure proper manufacturing techniques. Torsion tests are performed by applying rotational forces or by applying both compression and rotational forces. Types of torsion testing vary from product to product but can usually be classified as failure, proof, or product operation testing. See figure B.

Shear Strength: Shear is accomplished by exerting shear force (pressure) in the crosswise surface of the fastener until shear failure occurs. Shear force causes the two adjacent portions of the fastener to slide in opposite directions parallel to their contact surface. See figure C.

Pullout Performance: Pullout is the capacity of a fastener’s thread connection with a particular medium to remain intact and resist being pulled out of the medium. See figure D.

Pullover Performance: Pullover performance relates to the capacity of a fastener to resist the pulling of the fastened sheet material over the head of the fastener. The resistance to pullover is related to the strength and diameter of the fastener washer as well as the strength and thickness of the metal panel used. See figure E.

Knowing these terms, and how they differ, will help you in selecting the proper fastener for your next project. Need more help? Check out our Fastener Selection Guide.