When looking for ways to reduce waste, cost-conscious and environmentally aware manufacturers and consumers may consider reusing metric bolts and screws. But not all bolts and screws can be safely and effectively reinstalled after being removed from an assembly or component. In fact, an unequivocal “yes” is never the answer to the question of whether a fastener can be reused. Depending on the situation, the answer is always either “no” or “it depends.”
High-strength bolts that have been pre-tensioned into their proof load range – the point at which they permanently deform and do not “snap back” when relieved from their loads – should not be reused. This is the case in many applications, as structural and other bolts used in the manufacturing, construction, and automotive industries are commonly tightened to a torque value that creates a sufficient clamp force to prevent joint failure.
Tightening a nut onto a bolt causes the bolt to stretch slightly. Much like a spring, the bolt resists this stretching, and its tendency to return to its natural state creates clamping action between, say a cylinder head and a manifold, or two pieces of sheet-metal housing.
It is critical to the component’s operation that the amount of tension created holds the parts together strongly enough to prevent their separation by outside forces such as the machine’s vibration, the load stress generated during operation, gasket creep, temperature fluctuations, and more. Too much torque, however, can stretch the fastener too much, to the point where it chips, breaks, or yields. Bolts and screws are rated by their “proof load” – how much tension they can withstand before they fail. As a rule of thumb, torque a “clamp load” (also known as “preload”) 75 percent to 90 percent of the proof load is optimal.
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The establishment of the International Organization for Standardization (ISO) is based on the need to facilitate international trade by promoting development of universal standards. Having been in place for over a decade now, the ISO 9001:2008 Certification is a universal method used by both customers and companies to control the quality of output.
It is a framework of business management ensuring continued improvements in all aspects of the business. The external assessment on a regular basis ensures maintenance of these business practices.
Whether you’re a part-time hobbyist or a seasoned mechanic, there comes a time when you have an unidentified hole, bolt, or screw. To finish your assembly, you need to know exactly what size fastener you have, or what size fastener you need. The “guess and test” method can damage the threads on the fastener and in the hole. Worse yet, you could end up with something that seems to fit, but isn’t really the right size. When that happens, mechanical failure becomes a real risk.
Fortunately, screw thread callouts are a standardized system for determining the size, thread pitch, and length of a machine screw or hole. With this information, you can quickly get all of the information you need to ensure that your fastener fits perfectly into your assembly.
Set screws are one of those smaller metric fastener components that aren’t given as much attention as they deserve.
In spite of their lack of fame, they are available in a wide variety of different fabrications. They are also used in a variety of different applications ranging from simple tasks such as installing a door knob, to more complex ones like working on a space shuttle.
Any time an object needs to be affixed to some sort of shaft, a set screw is likely to be utilized. However, given the wide variety of applications that use set screws, you want to make sure that you are using the right one for your specific application.